[llvm] [RemoveDIs][NFC] Introduce DbgRecord base class [1/3] (PR #78252)

[Jeremy Morse via llvm-commits]

https://github.com/jmorse approved this pull request.

LGTM with some minor things inline to fiddle with. Am I right in thinking that there are effectively two levels of "kinds" to deal with -- kinds of DbgRecords and kinds of DPValues? And is that going to change in the later patches -- reason being that there's potential for people being confused by this, plus there's precedent in the rest of LLVM to have a single enum for each hierachy and use isa/dyn_cast/etc to distinguish them.

Starting to change all the names of all of these things, now that we've got a better handle on what's going on, sounds like a good idea.

https://github.com/llvm/llvm-project/pull/78252