This isn't a full fix, as the paint function does not handle this
either. But instead of getting the bitmap from the image source
immediately, follow the spec a bit more closely by creating the
CanvasPatern object with the ImageSource directly.
Fixes a crash for the 5 included WPT tests.
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
