In line with the ShadowRealm proposal changes in the WebIDL spec:
webidl#1437 and supporting changes in HTML spec.
This is required for ShadowRealms as they have no relevant settings
object on the shadow realm, so fixes a crash in the QueueingStrategy
test in this commit.
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
