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

[Shubham Sandeep Rastogi via llvm-commits]

rastogishubham wrote:

@OCHyams sorry about the squashing, I missed that in your previous comment. I will make sure I keep that in mind for the future

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