forEach, map, filter, some, every, find, findIndex, findLast,
findLastIndex and flatMap on a dynamic array, and through
Array.prototype.<method>.call on a native array, called the callback
without its thisArg, so `this` in the callback was not the second
argument. These methods now bind `this` to the thisArg, or undefined
when there is none, once per call, around all of the method's callbacks.
Chris Tate
928c30e908