[llvm] [RISCV][GISEL] Legalize G_ZEXT, G_SEXT, G_ANYEXT, G_SPLAT_VECTOR, and G_ICMP (PR #85938)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

I removed regbank selection and instruction selection from this patch to make the review smaller. I will post those as their own PRs.

https://github.com/llvm/llvm-project/pull/85938