Feature request: Generate function assist should use Self alias

When you have some code like

struct MyStruct {}

fn main() {
    let foo = MyStruct::from_list(&[0u32]);
}

And use the "generate function" assist on from_list, RA currently generates a function from_list with a signature like fn from_list(value: &[u32]) -> MyStruct in an impl block when it could also generate fn from_list(value: &[u32]) -> Self. I think the latter is generally preferred.

Locate the generate-function assist implementation and its tests, then trace how the return type is chosen for functions generated in an impl block. Update the behavior so this case uses Self instead of the concrete struct name, and add or adjust coverage for the example; done means the assist produces the requested signature without regressing other generated functions.