If `HTMLMarqueeElemnt.scrollAmount` or `HTMLMarqueeElemnt.scrollDelay`
is set to a value larger than 2147483647, then it should be set to its
default value.
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
