swift234

SIL: Fix type lowering to correctly handle concrete same-type constraints

When a dependent type is mapped into context, the result will either be
an archetype or a concrete type. The latter occurs if a same-type
constraint exists between the dependent type and the concrete type.

The logic to decide if a type should be passed directly or indirectly
was not handling this case if an interface type was passed down -- we
would just check if there was a class constraint present.

This resulted in mismatching conventions between an interface type and
its corresponding contextual type, which would trigger assertions.

Note that same-type constraints between generic parameters and concrete
types are still not supported for other reasons; the subject of the
constraint must still be an associated type of a generic parameter.

Fixes <rdar://problem/24687460>.