[llvm] [RISCV][GISEL] Legalize G_INSERT and G_EXTRACT for scalable vectors (PR #108220)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

The purpose of this patch is so that it can be used by #108250. I propose that we accept this patch so we can move #108250 through. Then, we should look to revise #108250 to not rely on G_INSERT and G_EXTRACT. I do not have the bandwidth to rewrite #108250 without G_INSERT and G_EXTRACT at the moment.

https://github.com/llvm/llvm-project/pull/108220