Add errors for unknown, stable and duplicate feature attributes
- Adds an error for unknown (lang and lib) features.
- Extends the lint for unnecessary feature attributes for stable features to libs features (this already exists for lang features).
- Adds an error for duplicate (lang and lib) features.
```rust
#![feature(fake_feature)] //~ ERROR unknown feature `fake_feature`
#![feature(i128_type)] //~ WARNING the feature `i128_type` has been stable since 1.26.0
#![feature(non_exhaustive)]
#![feature(non_exhaustive)] //~ ERROR duplicate `non_exhaustive` feature attribute
```
Fixes#52053, fixes#53032 and address some of the problems noted in #44232 (though not unused features).
There are a few outstanding problems, that I haven't narrowed down yet:
- [x] Stability attributes on macros do not seem to be taken into account.
- [x] Stability attributes behind `cfg` attributes are not taken into account.
- [x] There are failing incremental tests.
b239743753