Address FindTPL<tplName>.cmake inner find_package() calls finding TriBITS-installed <tplName>Config.camke files and add beginning of new examples '2' (#299, #427)

[bartlettroscoe]

This PR first adds a failing tests that basically reproduces the problems highlighted in bug report #427 in commit fb79c7f. The (what should be) super robust solution for this given in commits b4a6628 and b4a6628 and is is explained at the bottom of the TriBITS Users Guide section "How to use find_package() for a TriBITS TPL":

• https://github.com/TriBITSPub/TriBITS/blob/8fe2a49f6f045aa95801dd40aab0ae4ef7688a35/tribits/doc/guides/TribitsGuidesBody.rst#how-to-use-find_package-for-a-tribits-tpl

which is:

Therefore, to avoid having an installed TriBITS-generated HDF5Config.cmake
file, for example, being found by the inner call to find_package(HDF5 ...)
in the file FindTPLHDF5.cmake (which would be disastrous), TriBITS employs
two safeguards. First, TriBITS-generated <tplName>Config.cmake files are
placed into the build directory <buildDir>/external_packages/ and
installed into the directory <installDir>/lib/external_packages/ so they
will not be found by default when <buildDir>/cmake_packages and/or
<installDir>, respectively, are added to CMake_PREFIX_PATH. Also,
even if <installDir>/lib/external_packages or
<buildDir>/external_packages do get added to the search path somehow
(e.g. through CMAKE_INSTALL_PREFIX), the TriBITS framework will set the
variable TRIBITS_FINDING_RAW_<tplName>_PACKAGE_FIRST=TRUE before including
FindTPL<tplName>.cmake and there is special logic in the TriBITS-generated
<tplName>ConfigVersion.cmake file that will set
PACKAGE_VERSION_COMPATIBLE=OFF and result in find_package(<tplName>)
not selecting <tplName>Config.cmake. (It turns out that CMake's
find_package(<Package>) command always includes the file
<Package>ConfigVersion.cmake, even if no version information is passed to
the command find_package(<Package>). This allows special logic to be
placed in the file <Package>ConfigVersion.cmake to determine if
find_package(<Package>) will select a given <Package>Config.cmake file
that is in the search path based on a number of different criteria such as in
this case.)

Also in this PR:

• 6ff0323: Provide a first example of a FindTPL<tplName>.cmake file that writes a custom <tplName>Config.cmake file that uses find_dependency() with <tplName>_DIR set to find upstream external non-TriBITS package.
• 6f0e888: Added error message for find_pacakge(<Project> REQUIRED COMPONENTS <c0> <c1>) describing what packages were not present when finding a project's <Project>Config.cmake file with components and a test to ensure the right error message gets printed.
• Created the beginnings of TribitsExampleProject2 and TribitsExampleApp2 that will allow deeper testing with dependent TPLs so that I can finish implementing the move to modern CMake targets and stripping the old complex TriBITS logic (Move to modern CMake target-based propagation of build information #299).

[bartlettroscoe]

I will go ahead and do the merge and any reviews can take place post-merge. I need to address a known problem with MS Windows and then get this PR added to the TriBITS snapshot for trilinos/Trilinos#9894.