[LowerToAIE] Fix for non-deterministic error (observed with convolution)

[newling]

What was happening was

1. Value/Operation inserted into IRMapping
2. IRRewriter erased Value/Op
3. New Value/Op created with same address as erased Value/Op
4. Bad state: new Value/Op is a key in IRMapping, even though it was never added.

That's my analysis, at least. Either way, this change makes my failure rate go from 10/20 to 0/20.

An alternative to this PR might be to postpone erasing of ops even longer, so that only after all CoreOps have been processed are the ops erased.

[makslevental]

Isn't the "correct" thing to do to use Conversion instead of just an OperationPass? Like doesn't a conversion both handle the mapping for you and actually defer the erases (that last part is definitely true).

[makslevental]

I mean we should probably just merge this and be done with it because why rewrite a pass that we won't need soon.