feature: Add `destructure_struct_binding`
Adds an assist for destructuring a struct in a binding (#8673). I saw that #13997 has been abandoned for a while, so I thought I'd give it a go.
## Example
```rust
let foo = Foo { bar: 1, baz: 2 };
let bar2 = foo.bar;
let baz2 = foo.baz;
let foo2 = foo;
let fizz = Fizz(1, 2);
let buzz = fizz.0;
```
becomes
```rust
let Foo { bar, baz } = Foo { bar: 1, baz: 2 };
let bar2 = bar;
let baz2 = baz;
let foo2 = todo!();
let Fizz(_0, _1) = Fizz(1, 2);
let buzz = _0;
```
More examples in the tests.
## What is included?
- [x] Destructure record, tuple, and unit struct bindings
- [x] Edit field usages
- [x] Non-exhaustive structs in foreign crates and private fields get hidden behind `..`
- [x] Nested bindings
- [x] Carry over `mut` and `ref mut` in nested bindings to fields, i.e. `let Foo { ref mut bar } = ...` becomes `let Foo { bar: Bar { baz: ref mut baz } } = ...`
- [x] Attempt to resolve collisions with other names in the scope
- [x] If the binding is to a reference, field usages are dereferenced if required
- [x] Use shorthand notation if possible
## Known limitations
- `let foo = Foo { bar: 1 }; foo;` currently results in `let Foo { bar } = Foo { bar: 1 }; todo!();` instead of reassembling the struct. This requires user intervention.
- Unused fields are not currently omitted. I thought that this is more ergonomic, as there already is a quick fix action for adding `: _` to unused field patterns.
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