Fix the binder-swap transformation in OccurAnal
The binder-swap transformation needs to be iterated, as shown by #19581 (closed).
The fix is pretty simple, and is explained in point (BS2) of Note [The binder-swap substitution]
.
Net effect:
- sometimes, fewer simplifier iterations
- sometimes, more case merging
Test case in simplCore/should_compile/T19581
Fixes #19581 (closed).