no-var-before-return: add fixer

[ajafff]

Should be easy to implement.

Some things to consider:

function f() {
    var a = foo(), b = bar(a, a);
    return b;
}

function f() {
    var a = foo();
    return bar(a, a);
}

function f() {
    var a: {} = "foo"; // move annotation to funtion signature, iff this is the only return
    return a;
}

function f(): {} {
    return "foo";
}

[ajafff]

turn out to be not as easy as I thought. The fixer needs to handle destructuring as well