swift234

IRGen: Use metadata templates for non-generic types with fields of resilient type

Let's say that A and B defined in modules X and Y respectively.
This patch adds support for these two cases:

1) Fixed-layout struct A contains resilient struct B
2) Resilient struct A contains resilient struct B

In both cases:

a) Metadata access requires an accessor call
b) Fields of A do not have constant offsets, instead the offsets
   must be loaded from type metadata

A future patch will switch over to initializing the template in-place,
instead of heap-allocating a copy.