Instead of bothering the GC heap with a bunch of DOMRect allocations,
we can just pass around CSSPixelRect internally in many cases.
Before this change, we were generating so much DOMRect garbage that
we had to do a garbage collection *every frame* on the Immich demo.
This was due to the large number of intersection observers checked.
We still need to relax way more when idle, but for comparison, before
this change, when doing nothing for 10 seconds on Immich, we'd spend
2.5 seconds updating intersection observers. After this change, we now
spend 600 ms.
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
Now that the heap has no knowledge about a JavaScript realm and is
purely for managing the memory of the heap, it does not make sense
to name this function to say that it is a non-realm variant.
