Eagerly normalize `.await`'s `IntoFuture::Output`

The lack of this has caused an error when it diverges, because `shallow_resolve(ty).is_never()` was false. Given that we should switch to eager normalization anyway, like rustc, this makes sense to do.

Also switch the `shallow_resolve(ty).is_never()` to `resolve_vars_with_obligations(ty).is_never()`, because rustc uses this function.

And three drive-by changes:

 - Change referrals to Chalk in logging into next-solver;
 - In `setup_tracing()`, do not cache the existence of the env var. This function is not perf-sensitive, and caching it means it's more complicated than necessary to change it mid-execution.
 - Rearrange `expr_guaranteed_to_constitute_read_for_never()` a bit.