sagemathgh-37598: Sphinx extlinks for ecl, gap, giac, maxima, meson, ppl, qepcad, scip, singular, soplex
    
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We create a standard way to refer to the online manuals of these
packages, which are generated by tools other than Sphinx and therefore
cannot be linked to using Intersphinx.

This extends what has been already done with Pari.

Examples:
- [Examples in the Developer Guide](https://deploy-preview-37598--
sagemath.netlify.app/html/en/developer/sage_manuals#hyperlinks)

Fixes sagemath#27495.

Outside of the scope of this PR:
- adding such extlinks everywhere
- working with upstream projects to upgrade to better documentation
tools
- projects that can be linked to using Intersphinx; that's sagemath#37575
- any consideration how to link instead to local copies of those
manuals, whether installed from SPKG or system packages.

### 📝 Checklist

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- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

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URL: sagemath#37598
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe, Max Horn

src/doc/en/developer/sage_manuals.rst

@@ -200,6 +200,66 @@ by Sage, you can link toward it without specifying its full path:
      - ``:mathscinet:`MR0100971```
      - :mathscinet:`MR0100971`
 
+   * - :ref:`ECL <spkg_ecl>`
+     - ``:ecl:`Manipulating-Lisp-objects```
+     - :ecl:`Manipulating-Lisp-objects`
+
+   * -
+     - ``:common_lisp:`RENAME-PACKAGE <f_rn_pkg>```
+     - :common_lisp:`RENAME-PACKAGE <f_rn_pkg>`
+
+   * - :ref:`GAP <spkg_gap>`
+     - ``:gap:`Groups <chap39>```
+     - :gap:`Groups <chap39>`
+
+   * -
+     - ``:gap_package:`GAP package QuaGroup <quagroup/doc/chap0_mj.html>```
+     - :gap_package:`GAP package QuaGroup <quagroup/doc/chap0_mj.html>`
+
+   * - :ref:`Giac <spkg_giac>`
+     - ``:giac_cascmd:`gbasis <node280>```
+     - :giac_cascmd:`gbasis <node280>`
+
+   * -
+     - ``:giac_us:`Unary-functions```
+     - :giac_us:`Unary-functions`
+
+   * - :ref:`Maxima <spkg_maxima>`
+     - ``:maxima:`struve_h <index-struve_005fh>```
+     - :maxima:`struve_h <index-struve_005fh>`
+
+   * - :ref:`Meson <spkg_meson>`
+     - ``:meson:`install_subdir <Reference-manual_functions.html#install_subdir>```
+     - :meson:`install_subdir <Reference-manual_functions.html#install_subdir>`
+
+   * - :ref:`Pari <spkg_pari>`
+     - ``:pari:`lfungenus2```
+     - :pari:`lfungenus2`
+
+   * - :ref:`polymake <spkg_polymake>`
+     - ``:polymake:`matroid```
+     - :polymake:`matroid`
+
+   * - :ref:`PPL <spkg_ppl>`
+     - ``:ppl:`Linear_Expression <classParma__Polyhedra__Library_1_1 Linear__Expression>```
+     - :ppl:`Linear_Expression <classParma__Polyhedra__Library_1_1Linear__Expression>`
+
+   * - :ref:`QEPCAD <spkg_qepcad>`
+     - ``:qepcad:`QEPCAD: Entering formulas <user/EnterForm>```
+     - :qepcad:`QEPCAD: Entering formulas <user/EnterForm>`
+
+   * - :ref:`SCIP <spkg_scip>`
+     - ``:scip:`SCIPsolve <group__PublicSolveMethods>```
+     - :scip:`SCIPsolve <group__PublicSolveMethods>`
+
+   * - :ref:`Singular <spkg_singular>`
+     - ``:singular:`stdfglm <sing_358>```
+     - :singular:`stdfglm <sing_358>`
+
+   * - :ref:`SoPlex <spkg_soplex>`
+     - ``:soplex:`soplex::LinSolverRational <classsoplex_1_1SLinSolverRational>```
+     - :soplex:`soplex::LinSolverRational <classsoplex_1_1SLinSolverRational>`
+
 **http links:** copy/pasting a http link in the documentation works. If you want
 a specific link name, use ```link name <http://www.example.com>`_``
 

src/sage/algebras/quantum_groups/quantum_group_gap.py

@@ -6,9 +6,8 @@
 
 - Travis Scrimshaw (03-2017): initial version
 
-The documentation for GAP's QuaGroup package, originally authored by
-Willem Adriaan de Graaf, can be found at
-https://www.gap-system.org/Packages/quagroup.html.
+See the :gap_package:`documentation for GAP's QuaGroup package <quagroup/doc/chap0_mj.html>`,
+originally authored by Willem Adriaan de Graaf.
 """
 
 # ****************************************************************************

src/sage/combinat/designs/incidence_structures.py

@@ -1810,8 +1810,7 @@ def dual(self, algorithm=None):
 
         REFERENCE:
 
-        - Soicher, Leonard, Design package manual, available at
-          https://www.gap-system.org/Manuals/pkg/design/htm/CHAP003.htm
+        - Leonard Soicher, :gap_package:`Design package manual <design/htm/CHAP003.htm>`
         """
         if algorithm == "gap":
             libgap.load_package("design")

src/sage/groups/cubic_braid.py

@@ -274,8 +274,8 @@ def _richcmp_(self, other, op):
         :class:`FinitelyPresentedGroupElement` (via Gap) does not terminate
         in the case of more than 5 strands (not only infinite cases).
         On less than 5 strands comparison is not assumed to be deterministic
-        (see the :issue:`33498` and section 47.3-2 of the
-        `Gap Reference manual <https://www.gap-system.org/Manuals/doc/ref/chap47.html>`__).
+        (see the :issue:`33498` and :gap:`section 47.3-2 of the
+        Gap Reference manual <chap47>`).
 
         Therefore, the comparison is done via the Burau representation.
 

src/sage/groups/generic.py

@@ -1625,8 +1625,7 @@ def structure_description(G, latex=False):
     This methods wraps GAP's ``StructureDescription`` method.
 
     For full details, including the form of the returned string and the
-    algorithm to build it, see `GAP's documentation
-    <https://www.gap-system.org/Manuals/doc/ref/chap39.html>`_.
+    algorithm to build it, see :gap:`GAP's documentation <chap39>`.
 
     INPUT:
 

src/sage/groups/matrix_gps/finitely_generated_gap.py

@@ -223,8 +223,7 @@ def module_composition_factors(self, algorithm=None):
         Type ``G.module_composition_factors(algorithm='verbose')`` to get a
         more verbose version.
 
-        For more on MeatAxe notation, see
-        https://www.gap-system.org/Manuals/doc/ref/chap69.html
+        For more on MeatAxe notation, see :gap:`chap69`.
         """
         from sage.libs.gap.libgap import libgap
         F = self.base_ring()

src/sage/libs/gap/util.pyx

@@ -188,8 +188,8 @@ cdef initialize() noexcept:
     """
     Initialize the GAP library, if it hasn't already been
     initialized.  It is safe to call this multiple times. One can set
-    :envvar:`SAGE_GAP_MEMORY` to a particular value, as desribed in
-    `GAP Manual <https://www.gap-system.org/Manuals/doc/ref/chap3.html>`_
+    :envvar:`SAGE_GAP_MEMORY` to a particular value, as described in
+    the :gap:`GAP Manual <chap3>`.
     Specifically, the value is for `-s` and `-o` options.
 
     TESTS::

src/sage/misc/sagedoc.py

@@ -512,7 +512,21 @@ def process_dollars(s):
     'oeis': ('https://oeis.org/%s', 'OEIS sequence %s'),
     'doi': ('https://doi.org/%s', 'doi:%s'),
     'pari': ('https://pari.math.u-bordeaux.fr/dochtml/help/%s', 'pari:%s'),
-    'mathscinet': ('https://www.ams.org/mathscinet-getitem?mr=%s', 'MathSciNet %s')
+    'mathscinet': ('https://www.ams.org/mathscinet-getitem?mr=%s', 'MathSciNet %s'),
+    'common_lisp': ('https://www.lispworks.com/documentation/lw50/CLHS/Body/%s.htm', 'Common Lisp: %s'),
+    'ecl': ('https://ecl.common-lisp.dev/static/manual/%s.html', 'ECL: %s'),
+    'gap': ('https://docs.gap-system.org/doc/ref/%s_mj.html', 'GAP: %s'),
+    'gap_package': ('https://docs.gap-system.org/pkg/%s', 'GAP package %s'),
+    'giac_cascmd': ('https://www-fourier.ujf-grenoble.fr/~parisse/giac/doc/en/cascmd_en/%s.html', 'Giac: %s'),
+    'giac_us': ('https://www-fourier.ujf-grenoble.fr/~parisse/giac_us.html#%s', 'Giac API: %s'),
+    'maxima': ('https://maxima.sourceforge.io/docs/manual/maxima_singlepage.html#%s', 'Maxima: %s'),
+    'meson': ('https://mesonbuild.com/%s', 'Meson: %s'),
+    'polymake': ('https://polymake.org/doku.php/documentation/latest/%s', 'polymake: %s'),
+    'ppl': ('https://www.bugseng.com/products/ppl/documentation/user/ppl-user-1.2-html/%s.html', 'PPL: %s'),
+    'qepcad': ('https://www.usna.edu/CS/qepcadweb/B/%s.html', 'QEPCAD: %s'),
+    'scip': ('https://scipopt.org/doc/html/%s.php', 'SCIP: %s'),
+    'singular': ('https://www.singular.uni-kl.de/Manual/4-3-2/%s.htm', 'Singular: %s'),
+    'soplex': ('https://soplex.zib.de/doc/html/%s.php', 'SoPlex: %s'),
 }