Proof of concept: Automatically determine MUST_USE_PROPERTY/ATTRIBUTE

Hand meet glove #1449.
This is a super shitty implementation, but simply to get the discussion going.

Rather than manually determine attributes and properties, this does it automatically. Combined with #1449 this could be done at start-up if preferred (since we'd then have a fixed set of elements and attributes/properties). Using the same principle we can also determine the type of properties, but not for attributes (I think at least).

Supported by all browsers? Sure seems so, very quick testing in IE8 revealed no issues.

2 failed tests, but they are not indicative of a fundamental issue with this patch, simply "changing circumstances" that are incidentally addressed by my other recent PRs.