[llvm] A MMIWP Constructor Initialized with the move constructor of MMI (PR #98770)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Yes, the machine function map gets moved; but each machine function holds an internal reference to the original MMI and its context, and moving them makes those references stale.

Can we remove this reference from MachineFunction? Intuitively it shouldn't be necessary. A quick grep shows limited uses, and in contexts where it should be directly queryable from the PM

https://github.com/llvm/llvm-project/pull/98770