[CodeCompletion] Don't take opaque types subst map into account
for checking duplicated results from multiple type checker solutions.
e.g.
protocol Proto {}
struct Generic<T> {
func retProto() -> some Proto
}
func foo() -> Generic<T1>
func foo() -> Generic<T2>
foo().<COMPLETION>
The return type of `Geric<T1>.retProto()` and `Geric<T2>.retProto()` is
different, but they both spelled 'some Proto'. So IDE consumers don't
care the difference.
rdar://107669173
