In TaskQueue::take_tasks_matching(), we were not discarding tasks for
destroyed documents as we now do in ::take_first_runnable() since commit
c8baa6e179.
This fixes some occurrences of missing browsing contexts / active
documents in TraversableNavigable::destroy_top_level_traversable().
Previously, destroyed-document tasks were forced to be runnable to
prevent them from leaking in the task queue. Instead, discard them
during task selection so their callbacks never run with stale state.
This used to cause issues with a couple of `spin_until()`s in the past,
but since we've removed some of them that had to do with the document
lifecycle, let's see if we can stick closer to the spec now.
Documents that have never been associated with a browsing context will
never become "fully active" so we shouldn't schedule tasks in them since
they'll never run.
The inert temporary documents used for fragment parsing will never
become "fully active" and so any tasks associated with them will never
run. To avoid memory leaks, we now simply ignore any attempts to enqueue
tasks associated with such documents.
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
