swift234

SIL: Fix type lowering cache for interface types in abstraction pattern

If an abstraction pattern has interface types in it, we
already enforce that it was constructed with a generic
signature.

This generic signature is only used to answer questions
about the abstraction pattern's own formal type, and
not with the substituted type.

So only put type lowering cache entries in the dependent
cache if they contain interface types in the substituted
type. Otherwise, if only the abstraction pattern has
interface types in it, the entry can live in the
independent cache, allowing it to be looked up without
a pushGenericContext() / popGenericContext() call.

For correctness, we now have to store the generic signature
in the type key as well. Subsequent changes should reduce
the size of the cache, by lowering fewer archetypes.

NFC, since nothing uses this for now.