I missed where this change happened in the spec. The second half of
abort_the_ongoing_navigation() becomes a separate method, which is
slightly rearranged. I've placed this in Navigation instead of
NavigateEvent because of how many steps poke at the Navigation's
internals.
The text here includes the amendments I made in
https://github.com/whatwg/html/pull/11967 to correct a variable name.
A bonus is that we now actually populate the ErrorEvent instead of
leaving it blank.
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
