[llvm] [RemoveDIs][DebugInfo] Verifier and printing fixes for DPLabel (PR #83242)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Added various fixes to the verifier to make the parsing more permissive; I've copied the verifier tests, and they can be run with llvm-as, but only when parsing is enabled (the verifier first runs before we convert back at the end of parsing, so to verify the new format we have to read a file in the new format).

https://github.com/llvm/llvm-project/pull/83242