[DebugInfo] Skip ODRUniquing for mismatched tags

Otherwise, ODRUniquing would map some member method/variable MDNodes
to have enum type DIScope, resulting in invalid debug info and bad
DWARF.

- Add a Verifier check that when a 'scope:' operand is an ODR type that is not an enum.
- Makes ODRUniquing apply to only ODR types with the same tag so that the debuginfo/DWARF is well-formed.

Reviewed By: probinson, aprantl

Differential Revision: https://reviews.llvm.org/D111770