Integrate record accessors and modifiers where convenient.

Integrate record accessors and modifiers where convenient.

Limited to record types with:

- a defined predicate name we can pass to GUARANTEE, and
- no parent type so we can statically determine the field offsets.

Obviously it would be better if the compiler could do the flow
analysis to figure out where it can statically partially evaluate
RECORD-ACCESSOR and RECORD-MODIFIER, but, y'know, exercise for the
reader.