Fix assist and -> and_then parameter

[A4-Tacks]

Partial of #20967

• And fix fallback parentheses

Example

fn foo() {
    let foo = Some("foo");
    return foo.and$0(Some("bar"));
}

Before this PR

fn foo() {
    let foo = Some("foo");
    return foo.and_then(|| Some("bar"));
}

After this PR

fn foo() {
    let foo = Some("foo");
    return foo.and_then(|it| Some("bar"));
}

---

struct Func { f: fn() -> i32 }
fn foo() {
    let foo = true;
    let func = Func { f: || 2 };
    let x = foo.then$0(func.f);
}

Before this PR

request handler panicked: Failed to make ast node `syntax::ast::generated::nodes::CallExpr` from text const C: () = func.f();

After this PR

struct Func { f: fn() -> i32 }
fn foo() {
    let foo = true;
    let func = Func { f: || 2 };
    let x = foo.then_some((func.f)());
}