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

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

LGMT, thanks for adding the testcases!

I agree that the "sometimes reports the wrong variable" situation is a very significant improvement over the old "always infinite loop" situation; but this "convert a symbol to a variable name" step was completely missing from the old code, so I think it's relevant to mention that this commit implements it in a way that's not entirely correct.

I think it would be good to highlight this limitation with a FIXME comment (and perhaps a testcase), but I don't want to significantly delay the resolution of the infinite loop bug.

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