Feature request: Add field assist

[crumblingstatue]

struct Foo {
    field1: i32,
}

fn main() {
    let foo = Foo { field1: 42 };
    foo.field2/*add field assist requested here*/
}

The following would happen:

struct Foo {
    field1: i32,
    field2: /*editor focus and cursor jumps here*/,
}

Motivation: It can be tedious to jump to the type definition and type out the field name.
The user might not even remember the name of the type, so has to click on "go to type definition" on foo first.

[Veykril]

Duplicate of #4563