Fix explicit deref problems in closure capture
fix the `need-mut` part of #14562
Perhaps surprisingly, it wasn't unique immutable borrow. The code still doesn't emit any of them, and I think those won't happen in edition 2021 (which is currently the only thing implemented), since we always capture `&mut *x` instead of `&mut x`. But I'm not very sure about it.
Normalize associated types in paths in expressions
Part of #14393
When we resolve paths in expressions (either path expressions or paths in struct expressions), there's a need of projection normalization, which `TyLoweringContext` cannot do on its own. We've been properly applying normalization for paths in struct expressions without type anchor, but not for others:
```rust
enum E {
S { v: i32 }
Empty,
}
impl Foo for Bar {
type Assoc = E;
fn foo() {
let _ = Self::Assoc::S { v: 42 }; // path in struct expr without type anchor; we already support this
let _ = <Self>::Assoc::S { v: 42 }; // path in struct expr with type anchor; resolves with this PR
let _ = Self::Assoc::Empty; // path expr; resolves with this PR
}
}
```
With this PR we correctly resolve the whole path, but we need some more tweaks in HIR and/or IDE layers to properly resolve a qualifier (prefix) of such paths and provide IDE features that are pointed out in #14393 to be currently broken.
MIR episode 3
This PR adds lowering for try operator and overloaded dereference, and adds evaluating support for function pointers and trait objects. It also adds a flag to `analysis-stats` to show percentage of functions that it fails to emit mir for them, which is currently `20%` (which is somehow lying, as most of the supported `80%` are tests). The most offenders are closure (1975 items) and overloaded index (415 items). I will try to add overloaded index before monday to have it in this PR, and tackle the closure in the next episode.
