This has quite a lot of fall out. But the majority of it is just type or
UDL substitution, where the changes just fall through to other function
calls.
By changing property key storage to UTF-16, the main affected areas are:
* NativeFunction names must now be UTF-16
* Bytecode identifiers must now be UTF-16
* Module/binding names must now be UTF-16
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.
The DOM spec defines what it means for an element to be an "editing
host", and the Editing spec does the same for the "editable" concept.
Replace our `Node::is_editable()` implementation with these
spec-compliant algorithms.
An editing host is an element that has the properties to make its
contents effectively editable. Editable elements are descendants of an
editing host. Concepts like the inheritable contenteditable attribute
are propagated through the editable algorithm.
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
