Some initial normalization method changes
1. Rename `AtExt::normalize` to `QueryNormalizeExt::query_normalize` (using the `QueryNormalizer`)
2. Introduce `NormalizeExt::normalize` to replace `partially_normalize_associated_types_in` (using the `AssocTypeNormalizer`)
3. Rename `FnCtxt::normalize_associated_types_in` to `FnCtxt::normalize`
4. Remove some unused other normalization fns in `Inherited` and `FnCtxt`
Also includes one drive-by where we're no longer creating a `FnCtxt` inside of `check_fn`, but passing it in. This means we don't need such weird `FnCtxt` construction logic.
Stacked on top of #104835 for convenience.
r? types
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