[llvm] [AMDGPU] V_SET_INACTIVE optimizations (PR #98864)

[Carl Ritson via llvm-commits]

perlfu wrote:

- Rebase onto other WQM pass refactor
- Remove parts of #98562
- Remove semantics from V_SET_INACTIVE not used in WWM, always lower to COPY in these cases
- Optimize lowering of V_SET_INACTIVE to V_CNDMASK or V_MOV assuming WWM is available
- Update test IR where it appear to intend WWM behaviour for V_SET_INACTIVE but did not use WWM

https://github.com/llvm/llvm-project/pull/98864