We shouldn't generate NestedTypeNameMatch same-type constraints
between associated types we haven't realized yet.
Otherwise, since maybeResolveEquivalenceClass() can call
lookupNestedType() before looking up a PotentialArchetype, it
is possible that maybeResolveEquivalenceClass() will return
the newly-realized type even when resolutionKind is AlreadyKnown.
This can cause an infinite recursion in expandConformanceRequirement().
However, we don't really have to do this here at all, because if
a PotentialArchetype is registered with the same name later, we
will introduce the same-type constraint in addedNestedType().
It suffices for lookupNestedType() to return the best associated
type anchor and ignore the rest.
Fixes https://bugs.swift.org/browse/SR-14289 / rdar://problem/74876047.
