[llvm] [RISCV] Merge RISCVCoalesceVSETVLI back into RISCVInsertVSETVLI (PR #92869)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM, but please wait until early next week before landing.  If we have any fallout from the prior big change, it's good to avoid needing to revert a bunch of follow on stuff.  

https://github.com/llvm/llvm-project/pull/92869