Fix Trac #4345: simplifier bug
This is another long-standing bug, in which there was a possibility that a loop-breaker could lose its loop-breaker-hood OccInfo, and then the simplifer re-simplified the expression. Result, either non-termination or, in the case of #4345, an unbound identifier. The fix is very simple, in Id.transferPolyIdInfo. See Note [transferPolyIdInfo].