[clang] [llvm] Adapted MemRegion::getDescriptiveName to handle ElementRegions (PR #85104)

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https://github.com/NagyDonat requested changes to this pull request.

I strongly suspect that there are some situations where this commit would behave incorrectly (assert on legal code or print incorrect output). See inline comment for explanation and a suggested solution (that I did not test).

https://github.com/llvm/llvm-project/pull/85104