[flang] Catch name conflict between generic TBP and inherited non-generic

A generic procedure binding in an extended derived type may not have the
same name as a symbol inherited from an ancestor type unless that inherited
symbol is also a generic TBP.  Since generic names can be things like
"ASSIGNMENT(=)", name resolution doesn't use OkToAddComponent() for
generic TBPs, which would have caught this error as it does for other
symbols in derived types, so it must be special-cased.

Differential Revision: https://reviews.llvm.org/D145109