[llvm] [SPIR-V] Add implementation of G_SPLAT_VECTOR opcode and fix invalid types processing (PR #84766)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

https://github.com/llvm/llvm-project/pull/80378
G_SPLAT_VECTOR is only for scalable vectors. Does SPIR-V support scalable vectors?

https://github.com/llvm/llvm-project/pull/84766