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

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

LGTM.

Using this unit test framework is significantly cleaner than my suggestion that tries to work around the limitations of ArrayBoundV2.

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