There was a bug in the HTML proposal where a synthetic realm settings
object's principal realm was a shadow realm if there were nested shadow
realms, which this assertion catches more directly (rather than later
down the track, where it is used).
We were meant to also assert for this case, but we were previously
returning early.
This was removed from the ShadowRealm HTML spec integration PR after my
suggestion as it is not used anywhere, and I don't believe it would ever
need to be used in the future or by other specs.
An environment settings object will return a copy to the URL. From a
quick glance, we could probably make an environment settings object
return a reference to one, but let's just change this code to make
a copy since its not safe to rely on that.
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
Now that the heap has no knowledge about a JavaScript realm and is
purely for managing the memory of the heap, it does not make sense
to name this function to say that it is a non-realm variant.
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.
