Revert "[lldb][DebugNames] Only skip processing of DW_AT_declarations for class/union types"

and two follow-up commits. The reason is the crash we've discovered when
processing -gsimple-template-names binaries. I'm committing a minimal
reproducer as a separate patch.

This reverts the following commits:
- 51dd4eaa (#92328)
- 3d9d4852 (#93839)
- afe6ab75 (#94400)