Unlike ensure_web_prototype<T>(), the cached version doesn't require the
prototype type to be fully formed, so we can use it without including
the FooPrototype.h header. It's also a bit less verbose. :^)
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.
This is a subtype of `DOM::HTMLCollection` that only holds
`HTMLOptionElement`s. In this stub implementation only `item`,
`namedItem` and `length`, inherited from HTMLCollection, are exposed.
This is good enough for applications that only read the collection.
