[lldb][DWARF] Fix adding children to clang type that hasn't started definition. (#93839)

This fixes
https://github.com/llvm/llvm-project/pull/92328#issuecomment-2139339444


by not differentiating `DW_TAG_class_type` and `DW_TAG_structure_type`
in `UniqueDWARFASTTypeList`, because it's possible that DIE for a type
is `DW_TAG_class_type` in one CU but is `DW_TAG_structure_type` in a
different CU.

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Co-authored-by: Michael Buch <michaelbuch12@gmail.com>