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.
Ref-counted objects must not be stack allocated. Make DOM::Document's
constructor private to avoid this issue. (I wish we could mark classes
as heap-only..)
Note that there is currently no way to display them as we can't
currently clone nodes.
Adds special case for templates for dumping to console.
Doesn't add it to the DOM inspector as I'm not sure how to do it.
