Assist: Extract struct from function signature

When you select the signature of a function, you should have the ability to extract all or part of the function's parameters to a struct.


```
fn foo(bar: u32, baz: u32) { ... }
```
 ->
```
struct FooStruct {
     bar: u32,
     baz: u32,
}

fn foo(FooStruct) { ... }
```

This is something I would like to work on. Is the something that the rust-analyzer team would be interested in?