cleanup `TypeVerifier` We should merge it with the `TypeChecker` as we no longer bail in cases where it encounters an error since #111863. It's quite inconsistent whether a check lives in the verifier or the `TypeChecker`, so this feels like a quite impactful cleanup. I expect that for this we may want to change the `TypeChecker` to also be a MIR visitor :thinking: this is non-trivial so I didn't fully do it in this PR. Best reviewed commit by commit. r? `@compiler-errors` feel free to reassign however