An AK::String works fine for a USVString as a USVString is just a more
strict version of DOMString. Maybe we will have a different String type
for it in the future, but for now using an AK::String is fine and we do
not need this FIXME.
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
