contrib: rav1e: use internal dependencies and build vendor package

If the vendor package is not found, build it once and put it in the tarballs. So consecutive rebuilds between branches and targets will not cause a new download.

The vendor folder name used by rav1e is changed to not include a version number. The vendor folder will be rebuild/extracted again if versions change anyway.

Also enable back Rust on LLVM+Windows build since we switched the LLVM runners to LLVM15 in b16adfe7.