operand types are not normalized in MIR shims

[nikomatsakis]

In normal MIR, the types of local variables and things are fully normalized. However, in the MIR shims we construct, this is not always the case. We encountered this when fixing #45889, where it is necessary to normalize the types of operands in some cases to make the existing MIR typeck.

I'm not sure if this is a bug per se. Certainly once we move to lazy norm it will be fine. =) But it was surprising. For now we are normalizing (in the case of ADT constructors) during typeck.

cc @arielb1

[nikomatsakis]

cc @Nashenas88

[nikomatsakis]

I don't think this belongs in the milestone. This isn't really a problem, it's just causing us to run some extra normalizations -- or normalizations at an unexpected time.