CodeAction: Generate blanket trait implementation

[A4-Tacks]

Add a Code Action, Generate blanket trait implementation on trait define

• Generate This generic param
• Generate Self bounds to This
• Generate where-clause bounds
• Generate required methods, use todo!() fill

trait Foo: ToOwned
where
    Self::Owned: Default,
{
    fn foo(&self) -> i32;

    fn print_foo(&self) {
        println!("{}", self.foo());
    }
}

On trait Foo use Generate blanket trait implementation:

trait Foo: ToOwned
where
    Self::Owned: Default,
{
    fn foo(&self) -> i32;

    fn print_foo(&self) {
        println!("{}", self.foo());
    }
}
impl<This: ToOwned> Foo for This
where
    This::Owned: Default,
{
    fn foo(&self) -> i32 {
        todo!()
    }
}

[A4-Tacks]

@rustbot claim