[llvm] Reland "RegisterCoalescer: Add implicit-def of super register when coalescing SUBREG_TO_REG" (PR #134408)

[Sander de Smalen via llvm-commits]

sdesmalen-arm wrote:

Apologies for the noise, I merely rebased the patch onto latest upstream/main, which required changing the base commit.

https://github.com/llvm/llvm-project/pull/134408