We had a basic DORect implementation (which probably covered more cases). This
commit extends the implementation to be more complete:
- Add DOMRectReadOnly (which DOMRect inherits from)
- Add StructuredClone support to DOMRect and DOMRectReadOnly
- Make DOMRect and DOMRectReadOnly usable from Worker
DOMRect can be on the hot path with IntersectionObserver, so we maintain a
value-based data object (DOMRect.Data) for internal use (things returned to js
always have to be heap allocated (and always were, we're just more explicit
about this part now)).
7b8ea39164