Rewrite prefer-for-of rule

[nchen63]

fixes #1753

use walker instead of regex to determine usage of index variable
more validation, less fragile
more restrictive in suggesting for-of when multiple statements are in initializer, condition, or incrementer
allows for different ways of incrementing

old code had false positives:

    for(let x = 0; NOTX < arr.length; x++) {}

    for(let x = 0; x < arr.length; x--) {}

    for(let x = 0; x <= arr.length; x++) {}

    for(let x = 1; x < arr.length; x++) {}

    for(let x = 0; x < arr.length; x+=11) {}

and crashes on:

    for(let x = 0; true; x++) {}

    for(let x = 0; x < arr.length;) {}