[llvm] [RemoveDIs] Handle DPValues in LowerDbgDeclare (PR #73504)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

Reapplied original test RUN line, rebased patches, fixed conflicts by undoing changes in
```
llvm/test/Transforms/InstCombine/lower-dbg-declare.ll
llvm/test/Transforms/InstCombine/debuginfo.ll
llvm/test/Transforms/InstCombine/debuginfo-skip.ll
llvm/test/Transforms/InstCombine/dbg-scalable-store-fixed-frag.ll
llvm/test/DebugInfo/Generic/volatile-alloca.ll
```
- these tests now already have `--try-experiemtnal-debuginfo-iterators` in main.

https://github.com/llvm/llvm-project/pull/73504