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 used surprisingly often. For example, it is used by a core
YouTube library called Structured Page Fragments.
It allows you to manually dispatch an event with arbitrary data
attached to it.
The only thing missing from this implementation is the constructor.
This is because WrapperGenerator is currently missing dictionary
capabilities.