Auto merge of #42015 - nikomatsakis:chalk-trait-env-2, r=eddyb

remove interior mutability of type-flags

We were previously using the flags on `Ty<'tcx>` instances to do some ad-hoc caching schemes around things like `is_sized()`, `is_freeze()`, and `moves_by_default()`. This PR replaces those schemes with a proper query; the query key is based on the pair of a `(ParameterEnvironment<'tcx>, Ty<'tcx>)` pair. This is also intended to be a preliminary template for what trait-selection and projection will eventually look like.

I did some performance measurements. In the past, I observed a noticeable speedup (6%) for building rustc, but since I've rebased, the numbers appear to be more of a wash:

| Crate | Before | After | Percentage |
| --- | --- | --- | -- |
| syntax | 167s | 166s | 0.6% faster |
| rustc | 376s | 382s | 1.5% slower |

Some advantages of this new scheme:

- `is_sized` etc are proper queries
- we get caching across generic fns, so long as trait environment is identical
- dependency tracking is correct

0 files changed, 0 insertions, 0 deletions