Include MoltenVK files & dependencies in the crate

[repi]

Currently we have a magic build.rs file that syncs down a specific git revision of MoltenVK and then runs MoltenVK's even more magic fetch_dependencies.sh script which syncs down another 6-7 C++ dependencies from git, and then it is able to build.

All of this does work, but it is a bit fragile and ran into a specific problem where our license scanner in cargo-about didn't detect the additional dependencies and licenses of these downloaded dependencies because they simply do not exist in the .crate file, only exist in the target directory after build.rs have been run - which is hard to scan and find.

@MaikKlein @Jake-Shadle think we should try and change to have an explicit update script that we run manually to get down MoltenVK and all its dependencies and check it in, instead of build.rs.

[Jake-Shadle]

I would be ok with this as long as the update cadence of moltenvk was relatively low?

[repi]

We already pin it to latest official releases of MoltenVK since a while back, that have to be manually updated.

Looks like there have been 6-7 releases this year so not that often.