This is a monster patch that turns all EventTargets into GC-allocated
PlatformObjects. Their C++ wrapper classes are removed, and the LibJS
garbage collector is now responsible for their lifetimes.
There's a fair amount of hacks and band-aids in this patch, and we'll
have a lot of cleanup to do after this.
HTMLCollection is an awkward legacy interface from the DOM spec.
It provides a live view of a DOM subtree, with some kind of filtering
that determines which elements are part of the collection.
We now return HTMLCollection objects from these APIs:
- getElementsByClassName()
- getElementsByName()
- getElementsByTagName()
This initial implementation does not do any kind of caching, since that
is quite a tricky problem, and there will be plenty of time for tricky
problems later on when the engine is more mature.
