EventLoopPluginSerenity was the only implementation of the abstract
EventLoopPlugin base class. Its methods simply wrapped Core::EventLoop
calls with GC function unwrapping.
Remove the virtual dispatch by making EventLoopPlugin concrete and
absorbing the EventLoopPluginSerenity implementation directly.
TimerSerenity was the only implementation of the abstract Timer base
class. It simply wrapped a Core::Timer and delegated every method.
Remove the virtual dispatch by making Timer concrete and absorbing
the TimerSerenity implementation directly. Timer::create() now
allocates on the GC heap directly instead of going through
EventLoopPlugin::create_timer().
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
