Merge #11461

11461: Extract struct from enum variant filters generics r=jo-goro a=jo-goro

Fixes #11452.

This PR updates extract_struct_from_enum_variant. Extracting a struct `A` form an enum like
```rust
enum X<'a, 'b> {
    A { a: &'a () },
    B { b: &'b () },
}
```
will now be correctly generated as
```rust
struct A<'a> { a: &'a () }

enum X<'a, 'b> {
    A(A<'a>),
    B { b: &'b () },
}
```
instead of the previous
```rust
struct A<'a, 'b>{ a: &'a () } // <- should not have 'b

enum X<'a, 'b> {
    A(A<'a, 'b>),
    B { b: &'b () },
}
```

This also works for generic type parameters and const generics.

Bounds are also copied, however I have not yet implemented a filter for unneeded bounds. Extracting `B` from the following enum
```rust
enum X<'a, 'b: 'a> {
    A { a: &'a () },
    B { b: &'b () },
}
```
will be generated as
```rust
struct B<'b: 'a> { b: &'b () } // <- should be `struct B<'b> { b: &'b () }`

enum X<'a, 'b: 'a> {
    A { a: &'a () },
    B(B<'b>),
}
```

Extracting bounds with where clauses is also still not implemented.

Co-authored-by: Jonas Goronczy <goronczy.jonas@gmail.com>