[vcpkg] Add commands to maintain and verify versions db integrity

[vicroms]

This PR will add new commands to help maintain the version files up-to-date.

• Command to verify version files.
• Command to verify baseline file.
• Command to update versions and baseline files.
• Add end-to-end tests
• e2e test for ci-verify-versions to catch changes to the git sha within a single version
• Rename $x-default-baseline to "builtin-baseline" and check it is not used without the versions feature enabled
• Rename the field in baseline files to "baseline"
• Direct actionable messages for any failures reported by ci-verify-versions
• Check versions/ directory in
• Enable new CI checks

Name of commands is up for discussion.

vcpkg x-ci-verify-versions

This command verifies that each port:

• Has a corresponding version file in ${VCPKG_ROOT}/port_versions/${prefix}-/${port_name}.json
• The file contains a versions array.
• The top entry in the versions array matches the current version of the port.
• The local SHA matches the one in the git-tree property.
• The baseline file exists.
• The baseline version matches the current local version and the latest version in the db files.

This command will run as part of CI once the port_versions files have been merged.

vcpkg x-add-version ${port name}

Sets the current version in baseline.json to the version of the port in the ports directory; also adds the version to the corresponding versions file.

Drive-by changes:

• Changes to BaselineDeserializer
  • Changed return type from VersionT to SchemedVersion. This is necessary for updating the baseline file correctly with x-add-version.
• Changes to x-history:
  • Removed port version splitting.
  • Output to file with --output.
• Changes to generatePortVersions.py:
  • Parallelized generation. NOTE: Requires setting GIT_OPTIONAL_LOCKS=0 to avoid crashes.
  • Removed baseline.json generation.
• Changes to generateBaseline.py:
  • Generate from existing files in port_versions since calling x-package-info is infinitely slow.
  • Sped up execution 200-fold.

[vicroms]

We now check that local git-tree objects match those in the db files.

FAIL: zziplib
Found the following errors:
Error: Git tree-ish object for version `0.13.71` in `D:\vcpkg\port_versions\z-\zziplib.json` does not match local port files.
        Local SHA: 8171b5d16b817dabe3a1e0dfc711f2aa556b7a4e
         File SHA: 46d8c438267ece7a8e8ca0079896b25e579a845d

[ras0219]

I may be missing some subtleties w.r.t. the interesting return value from load_baseline_versions() and I haven't looked at the consumers of this function yet, however:

Why does the processing of port_versions/baseline.json potentially cause this section to be short-circuited? It seems that this function should:

1. if baseline_identifier is empty, return {}
2. if baseline_identifier is "default", parse the builtin baseline json and return that (or fail)
3. otherwise, try to check out baseline_identifier and parse from that.

If so, I'd expect a top-level if() to make that clearer.

[vicroms]

I'm not sure what is the actual use case for empty baseline_identifier. I just tried to preserve existing behavior.