Add an implementation of Default for Heap<*mut T>.
We should be able to create a default value for any Heap<*mut T> where *mut T implements GCMethods<*mut T> and Copy, not just for Heap<*mut JSObject>.
Add an implementation of Default for Heap<*mut T>.
We should be able to create a default value for any Heap<*mut T> where *mut T implements GCMethods<*mut T> and Copy, not just for Heap<*mut JSObject>.
