[lldb][DebugNames] Only skip processing of DW_AT_declarations for class/union types (#94400)

This is a follow-up of
https://github.com/llvm/llvm-project/pull/92328#issuecomment-2145849441

Clang attaches `DW_AT_declaration` to static inline data members and
`dsymutil` indexes these constants. Skipping these caused the expression
evaluator to fail to find such constants when using DWARFv5.

Fixes `TestConstStaticIntegralMember.py` on DWARFv5.