Support non-trait methods delegation

[50U10FCA7]

Background

Using delegation without trait:

struct MyField1;
struct MyField2;
enum MyEnum {
    Field1(MyField1),
    Field2(MyField2),
}

impl MyField1 { fn do_something(&self) -> i32 { 1 } }
impl MyField2 { fn do_something(&self) -> i32 { 2 } }
#[delegate]
impl MyEnum { fn do_something(&self) -> i32; }

Problem to solve

Delegation of methods with the same signature not represented as part of some trait.