Fix some TryEnum reference assists

[A4-Tacks]

• Fix convert_to_guarded_return
• Fix replace_let_with_if_let
• Fix replace_if_let_with_match

Example

fn foo() -> &'static Option<i32> {
    &None
}

fn main() {
    let x$0 = foo();
}

Before this PR

Assist not applicable

After this PR

fn foo() -> &'static Option<i32> {
    &None
}

fn main() {
    let Some(x) = foo() else { return };
}

---

fn main(action: Action) {
    $0let x = compute();
}

fn compute() -> &'static Option<i32> { &None }

Before this PR

fn main(action: Action) {
    if let x = compute() {
    }
}

fn compute() -> &'static Option<i32> { &None }

After this PR

fn main(action: Action) {
    if let Some(x) = compute() {
    }
}

fn compute() -> &'static Option<i32> { &None }

---

fn foo(x: &Option<i32>) {
    $0if let Some(x) = x {
        println!("{}", x)
    } else {
        println!("none")
    }
}

Before this PR

fn foo(x: &Option<i32>) {
    match x {
        Some(x) => println!("{}", x),
        _ => println!("none"),
    }
}

After this PR

fn foo(x: &Option<i32>) {
    match x {
        Some(x) => println!("{}", x),
        None => println!("none"),
    }
}