[llvm] [SystemZ, DebugInfo] Support InstrRef-based Debug Value Tracking in the SystemZ backend (PR #132415)

[Jonas Paulsson via llvm-commits]

JonPsson1 wrote:

An inlined question above, and some suggestions:

- Probably best to pre-commit side-issues that were discovered and not strictly related (pass-initialization, asm comments). Makes the diff here smaller and also separate in case of any future revert.

- The calls to substituteDebugValuesForInst are self-explanatory, so not sure if a comment is needed before each call.

Have not looked too much at the tests.

https://github.com/llvm/llvm-project/pull/132415