* [vcpkg] Refactor out abi_tags_from_pre_build_info()
* [vcpkg] Track Windows toolchain file in triplet hash
* [vcpkg] Improve error messages when constructing PreBuildInfo
* [vcpkg] Extract InstallPlanAction::BuildAbiInfo
* [vcpkg] Extract Build::EnvCache and private-impl VcpkgPaths
* [vcpkg] Enable compiler hash detection when binarycaching is enabled
* [vcpkg] Downgrade warning about missing ABI keys
When binarycaching is not enabled, this warning is spurious and provides no user value.
* [vcpkg] Cleanup
* [vcpkg] Refactor compiler tracking into triplet abi computation
Move several static global caches into VcpkgPaths/EnvCache.
Add feature flag 'compilertracking' to enable the new feature.
* [vcpkg] Refactor out PreBuildInfo::using_vcvars()
Move VcpkgTripletVar into build.cpp because it is not used outside that file.
* [vcpkg] Address some code analysis warnings
Co-authored-by: Robert Schumacher <roschuma@microsoft.com>
