[RISCV][TII] Add and use new hook to optimize/canonicalize instructions after MachineCopyPropagation#137973

asb merged 25 commits intollvm:mainllvm/llvm-project:mainfrom

asb:2025q2-riscv-optimize-instruction-hookasb/llvm-project:2025q2-riscv-optimize-instruction-hookCopy head branch name to clipboard