Add ide-assist: inline as closure

[A4-Tacks]

fn foo() { println!("Hello, World!"); }
fn main() {
    let _ = foo$0;
}

->

fn foo() { println!("Hello, World!"); }
fn main() {
    let _ = || { println!("Hello, World!"); };
}

[A4-Tacks]

r?

[rustbot]

Error: Parsing assign command in comment failed: ...'' | error: specify user to assign to at >| ''...

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