This reverts commit 6f685ffa.

Remove Ty prefix from Ty{Adt|Array|Slice|RawPtr|Ref|FnDef|FnPtr|Dynamic|Closure|Generator|GeneratorWitness|Never|Tuple|Projection|Anon|Infer|Error}

Types will no longer default to `()`, instead always defaulting to `!`.
This disables the associated warning and removes the flag from TyTuple

In particular:

- `fully_normalize_monormophic_ty` => `normalize_erasing_regions`
- `normalize_associated_type_in_env` => `normalize_erasing_regions`
- `fully_normalize_associated_types_in` => `normalize_erasing_regions`
- `erase_late_bound_regions_and_normalize` => `normalize_erasing_late_bound_regions`

Adds support for immovable generators. Move checking of invalid borrows across suspension points to borrowck. Fixes #44197, #45259 and #45093.

Previously a `Symbol` was stored there, but this ended up causing hash
collisions in situations that otherwise shouldn't have a hash collision. Only
the symbol's string value was hashed, but it was possible for distinct symbols
to have the same string value, fooling various calcuations into thinking that
these paths *didn't* need disambiguating data when in fact they did!

By storing `InternedString` instead we're hopefully triggering all the exising
logic to disambiguate paths with same-name `Symbol` but actually distinct
locations.

Renames TyTrait to TyDynamic.

Associated type normalization is inhibited by higher-ranked regions.
Therefore, every time we erase them, we must re-normalize.

I was meaning to introduce this change some time ago, but we used
to erase regions in generic context, which broke this terribly (because
you can't always normalize in a generic context). That seems to be gone
now.

Ensure this by having a `erase_late_bound_regions_and_normalize`
function.

Fixes #37109 (the missing call was in mir::block).