Warn on classic mode build failure if version constraints weren't met

[ras0219-msft]

This PR adds tracking for version constraints in classic mode so that they can be displayed to the user in case of a build failure. While it is by design that classic mode does not force users to rebuild dependencies that are out-of-date, knowing the version constraints is a big help for debugging.

The output could be rough in certain circumstances; it will display every non-identical broken constraint and won't deduplicate 'similar' ones. For example, if the immediate dependencies list contains 3 references to curl with constraints >= 2, >= 2, and >= 3, on build failure this would display two messages (one for >= 2 and one for >= 3). This more complex deduplication is challenging to prove correct because we don't have schema information for installed packages. That said, it seems reasonably pathologic to have multiple non-identical constraints in the same package manifest.

Finally, this only displays for install commands -- it does not display for any other command (e.g. build, ci, x-set-installed).

Diff from e2e test:

 [end-to-end-tests.ps1] [1/1] Running suite /workspaces/vcpkg-tool/azure-pipelines/end-to-end-tests-dir/classic-versions.ps1
 /workspaces/vcpkg-tool-build/vcpkg --triplet x64-linux --x-buildtrees-root=/workspaces/vcpkg-tool/testing/testing/buildtrees --x-install-root=/workspaces/vcpkg-tool/testing/testing/installed --x-packages-root=/workspaces/vcpkg-tool/testing/testing/packages --overlay-ports=/workspaces/vcpkg-tool/azure-pipelines/e2e_ports/overlays --overlay-triplets=/workspaces/vcpkg-tool/azure-pipelines/e2e_ports/triplets install classic-versions-b
 Computing installation plan...
 found constraint violation: warning: dependency classic-versions-a:x64-linux was expected to be at least version 2, but is currently 1.
 The following packages will be built and installed:
   * classic-versions-a[core]:x64-linux -> 1 -- /workspaces/vcpkg-tool/azure-pipelines/e2e_ports/overlays/classic-versions-a
     classic-versions-b[core]:x64-linux -> 1 -- /workspaces/vcpkg-tool/azure-pipelines/e2e_ports/overlays/classic-versions-b
 Additional packages (*) will be modified to complete this operation.
 Detecting compiler hash for triplet x64-linux...
 Restored 1 packages from /workspaces/.cache/vcpkg in 1.506 ms. Use --debug to see more details.
 Installing classic-versions-a:x64-linux... (1/2)...
 Elapsed time to handle classic-versions-a:x64-linux: 547.1 us
 Installing classic-versions-b:x64-linux... (2/2)...
 Building classic-versions-b[core]:x64-linux...
 -- Installing port from location: /workspaces/vcpkg-tool/azure-pipelines/e2e_ports/overlays/classic-versions-b
 CMake Error at /workspaces/vcpkg-tool/azure-pipelines/e2e_ports/overlays/classic-versions-b/portfile.cmake:1 (message):
   FATAL_ERROR
 Call Stack (most recent call first):
   scripts/ports.cmake:145 (include)
 
 
+warning: dependency classic-versions-a:x64-linux was expected to be at least version 2, but is currently 1.
 error: building classic-versions-b:x64-linux failed with: BUILD_FAILED
 Please ensure you're using the latest portfiles with `git pull` and `./vcpkg update`.
 Then check for known issues at:
   https://github.com/microsoft/vcpkg/issues?q=is%3Aissue+is%3Aopen+in%3Atitle+classic-versions-b
 You can submit a new issue at:
   https://github.com/microsoft/vcpkg/issues/new?template=report-package-build-failure.md&title=[classic-versions-b]+Build+error
 including:
   package: classic-versions-b[core]:x64-linux -> 1
     vcpkg-tool version: 2999-12-31-unknownhash-debug
     vcpkg-scripts version: 9e46bb072 2022-03-02 (5 weeks ago)
 
 Additionally, attach any relevant sections from the log files above.

While implementing this, I identified a regression introduced in #322 where VersionScheme::String's were being compared lexographically. I've reverted this to the intended behavior (either eq or unk) and added tests covering this case.