[llvm] [RegisterCoalescer] Deferring deletion of instructions in `ErasedInstrs` until the end of an iteration (PR #79820)

[Quentin Dian via llvm-commits]

DianQK wrote:

Ping~

Though I know very little about this part. But I think this at least fixes the crash, with no other regressions.

https://github.com/llvm/llvm-project/pull/79820