[llvm] [NFC] Move DroppedVariableStats to its own file and redesign it to be extensible. (PR #115563)

[Orlando Cazalet-Hyams via llvm-commits]

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

LGTM - before committing can you please see if any of the fields in the base class can be made private instead of protected (I forgot to look at those while looking at the access specifiers for the member functions).

I'd also like to gently point out that you squashed your changes again (see my previous comment - this makes it more time consuming and difficult to review your updates).

https://github.com/llvm/llvm-project/pull/115563