[llvm] [NFC] Add GIntrinsic::setIntrinsicID (PR #106236)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> you have to notify observers in GiSel.

But not when erasing and replacing it with a new instruction, I guess? So, the "right" way for replacing one intrinsic with another is to really create a new one, even if rest of the properties are intended to stay the same? It seems that the base `MachineInstr` class supports mutation as well.

https://github.com/llvm/llvm-project/pull/106236