Metadata for an instance of a type is resolved by extracting it from an
instance of the class. When doing method lookup for an instance method
of a resilient class, the lowered self value was being obtained from the
list of arguments directly by indexing. That does not apply to async
functions where self is embedded within the async context. Here, the
self parameter is extracted from the async context so that the metadata
can in turn be extracted from it.
rdar://problem/71260862
