By doing that we avoid lots of `PropertyKey` -> `Value` -> `PropertyKey`
transforms, which are quite expensive because of underlying
`FlyString` -> `PrimitiveString` -> `FlyString` conversions.
10% improvement on MicroBench/object-keys.js
This is *extremely* common on the web, but barely shows up at all in
JavaScript benchmarks.
A typical example is setting Element.innerHTML on a HTMLDivElement.
HTMLDivElement doesn't have innerHTML, so it has to travel up the
prototype chain until it finds it.
Before this change, we didn't cache this at all, so we had to travel
the prototype chain every time a setter like this was used.
We now use the same mechanism we already had for GetBydId and cache
PutById setter accesses in the prototype chain as well.
1.74x speedup on MicroBench/setter-in-prototype-chain.js
PlatformObjects with named properties does not qualify as 'has own
property' just by virtue of a named property existing.
This fixes at least one WPT test, which is imported.
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
