[vcpkg] Avoid computing triplet ABIs for editable packages

[ras0219]

This PR delays computation of abi_info.triplet_abi until after we perform a check for conditions that would disable computation of a package abi. This can save several seconds in the port inner-dev loop.

The specific examples of this case are --editable and --head, which will both disable our ability to compute ABIs. Furthermore, if a package without an ABI is installed, all transitive consumers also cannot have their ABIs computed.

Before:

PS C:\src\vcpkg> vcpkg install zlib:x64-windows --editable
Computing installation plan...
The following packages will be built and installed:
    zlib[core]:x64-windows
Detecting compiler hash for triplet x64-windows...
Starting package 1/1: zlib:x64-windows
Building package zlib[core]:x64-windows...
-- Using cached C:/src/vcpkg/downloads/zlib1211.tar.gz
-- Using source at C:/src/vcpkg/buildtrees/zlib/src/1.2.11-63309e48e5
-- Configuring x64-windows
...

After:

PS C:\src\vcpkg> vcpkg install zlib:x64-windows --editable
Computing installation plan...
The following packages will be built and installed:
    zlib[core]:x64-windows
Starting package 1/1: zlib:x64-windows
Building package zlib[core]:x64-windows...
-- Using cached C:/src/vcpkg/downloads/zlib1211.tar.gz
-- Using source at C:/src/vcpkg/buildtrees/zlib/src/1.2.11-63309e48e5
-- Configuring x64-windows
...

+@qis who may be particularly happy about this change :)

[BillyONeal]

Should this have a test?

[ras0219]

Adding a test would require mocking System::cmd_execute() and friends; I think that would be too large of an infrastructure change for now given the size of this PR.

[BillyONeal]

Adding a test would require mocking System::cmd_execute() and friends;

I don't mean a unit test, I mean in the e2e tests.

[qis]

@ras0219 Works as advertised. Thank you!

[ras0219-msft]

/azp run

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