Rollup merge of #81496 - guswynn:expected_async_block, r=oli-obk

Rollup merge of #81496 - guswynn:expected_async_block, r=oli-obk

name async generators something more human friendly in type error diagnostic

fixes #81457

Some details:

1. I opted to load the generator kind from the hir in TyCategory. I also use 1 impl in the hir for the descr
2. I named both the source of the future, in addition to the general type (`future`), not sure what is preferred
3. I am not sure what is required to make sure "generator" is not referred to anywhere. A brief `rg "\"generator\"" showed me that most diagnostics correctly distinguish from generators and async generator, but the `descr` of `DefKind` is pretty general (not sure how thats used)
4. should the descr impl of AsyncGeneratorKind use its display impl instead of copying the string?