This is required to return original references to the shaders attached
to a program from getAttachedShaders. This is required for Figma (and
likely all other Emscripten compiled applications that use WebGL) to
get it's own generated shader IDs from the shaders returned from
getAttachedShaders.
This way we could be sure that context object won't be deallocated
before any of the objects that belong to it.
Having a context pointer is also going to be used in upcoming changes
to generate an INVALID_OPERATION error if an object does not belong to
the context it's being used in.
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
