* Integrate support for building with dependencies from vcpkg
Configure the build using -DUSE_VCPKG=ON to use vcpkg. By default
recommended triplets targeting the OS versions official builds support
are used. You can opt out of this with -DUSE_RECOMMENDED_TRIPLETS=OFF.
* Add the vcpkg manifest
* Fetch vcpkg with FetchContent if we don't have it
* macOS cross compiling fixes
- can't use the x86_64 one as host triplet on arm64 because building Qt
fails for whatever reason. Because of course it does :D
- vcpkg doesn't always like periods in triplet names so removed those
* x86_64 macOS should also use its recommended target when building arm64 builds
