Allow Extract Constant in expression-bodied arrow functions

[amcasey]

const f = () => 1 + [#|(2 + 3)|] + 4;

Expected:

const f = () => {
    const newLocal = (2 + 3);
    return 1 + newLocal + 4;
};

We can detect this scenario, but ChangeTracker doesn't support overlapping transformations (i.e. substituting newLocal into the expression and then putting the result into a return statement).