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
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.
