[llvm] [NFC] Add DIExpression::calculateFragmentIntersect (PR #97738)

[Stephen Tozer via llvm-commits]

https://github.com/SLTozer commented:

`calculateFragmentIntersect` took a bit of time to properly parse, not sure I have any suggestions to improve the clarity right now (besides a minor naming suggestion); other than that this LGTM.

https://github.com/llvm/llvm-project/pull/97738