[llvm] [RemoveDIs] Add DPLabels support [3a/3] (PR #82633)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

Removed --try-experimental-debuginfo-iterators from tests. For posterity, this patch stimulates the following tests:
```
llvm/test/CodeGen/Generic/live-debug-label.ll
llvm/test/CodeGen/MIR/X86/branch-folder-with-label.mir
llvm/test/CodeGen/PowerPC/debug-label-fast-isel.ll
llvm/test/DebugInfo/Generic/PR37395.ll
llvm/test/DebugInfo/Generic/debug-label-inline.ll
llvm/test/DebugInfo/Generic/debug-label-mi.ll
llvm/test/DebugInfo/Generic/debug-label-opt.ll
llvm/test/DebugInfo/Generic/debug-label.ll
llvm/test/DebugInfo/X86/debug-label-unreached.ll
llvm/test/DebugInfo/X86/live-debug-vars-nodebug.ll
llvm/test/Transforms/HotColdSplit/split-out-dbg-label.ll
llvm/test/Transforms/SimplifyCFG/bbi-23595.ll
llvm/test/Transforms/SpeculativeExecution/PR46267.ll
llvm/test/Transforms/Util/strip-nonlinetable-debuginfo-labels.ll
```

https://github.com/llvm/llvm-project/pull/82633