Adapted MemRegion::getDescriptiveName to handle ElementRegions (#85104)

Fixes https://github.com/llvm/llvm-project/issues/84463



Changes:
- Adapted MemRegion::getDescriptiveName
- Added unittest to check name for a given clang::ento::ElementRegion
- Some format changes due to clang-format

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Co-authored-by: Andreas Steinhausen <andreas.steinhausen@concenrio.io>
Co-authored-by: Balazs Benics <benicsbalazs@gmail.com>