[vcpkg] Prefer STREQUAL over MATCHES

[SunBlack]

Avoid using CMake's well-known slow regex engine if it is not necessary

Used the regex if.*MATCHES "\^[\w\s]*\$" to find all occurrences.

[JackBoosY]

I don't think we're using regex because it's too slow.
cc @strega-nil-ms @ras0219-msft

[JackBoosY]

Since it's full keyword regex. I think that's correct.

[BillyONeal]

These changes are all improvements, but not worth forcing everyone to rebuild the world over, as an edit to ports.cmake will do. As a result, we have tagged this with "world-rebuild" to potentially roll up into other changes that would affect that file.

However, the changes to buildsystems/vcpkg.cmake will not cause a world rebuild, so if you want to create a second PR with only those changes because you want those effects early, that would be OK. (Of course, given that this is just a code cleanup I doubt it's worth it to you)

[BillyONeal]

Sorry, I've just been informed the correct tag is "next-rollup" rather than "world-rebuild"; the latter is about PRs in progress while this PR is otherwise ready-to-merge.

[ras0219-msft]

LGTM, thanks for the improvement!