Tame Promise.resolve

[mhofman]

@erights's intention for Promise.resolve was that it'd be safe against evil promises and callbacks. To quote #1126:

My original intention on tc39 was that an expression like

Promise.resolve(p).then(whatever);

protect the code it appears in from reentrancy attacks no matter what p is. IOW, even if p and whatever are provided by an adversary, that adversary should not be able to get of their choosing to run within the caller's turn. However, this was attackable by installing a then function` as an own property on a genuine promise.

That PR explored a way to do this through a patched Promise.prototype.constructor, but we realized that was not tenable. However it seems like simply taming Promise.resolve might be sufficient. There is an analysis in the comments of that issue, but it hasn't been double-checked.