[llvm] [SPIRV] Add legalization for long vectors (PR #169665)

[Dmitry Sidorov via llvm-commits]

https://github.com/MrSidims commented:

The approach is LGTM, thanks!

Probably a test is missing for either shader with vector length > 4 or kernel with length > 16

https://github.com/llvm/llvm-project/pull/169665