We weren't doing this before either, but through a slightly sneaky
mechanism: we had overridden Cell::initialize() in
ShadowRealmGlobalScope as a no-op.
Instead of that, do the same thing Window and Worker globals do and
make all of the globals that inherit UniversalGlobalScopeMixin opt
out of WEB_SET_PROTOTYPE_FOR_INTERFACE in EventTarget::initialize().
These interfaces are exposed on *, meaning it should work for workers
and our newly added shadow realm global object by being stored on the
universal global scope mixin.
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
The main motivation behind this is to remove JS specifics of the Realm
from the implementation of the Heap.
As a side effect of this change, this is a bit nicer to read than the
previous approach, and in my opinion, also makes it a little more clear
that this method is specific to a JavaScript Realm.
