This reworks EventHandler so text insertion, backspace, delete and
return actions are now handled by the Editing API. This was the whole
point of the execCommand spec, to provide an implementation of both
editing commands and the expected editing behavior on user input.
Responsibility of firing the `input` event is moved from EventHandler to
the Editing API, which also gets rid of duplicate events whenever
dealing with `<input>` or `<textarea>` events.
The `beforeinput` event still needs to be fired by `EventHandler`
however, since that is never fired by `execCommand()`.
When the return key is pressed, we try to handle it as a commit action
for input elements. However, we would then go on to actually insert the
return key's code point (U+000D) into the input element. This would be
sanitized out, but would leave the input element in a state where it
thinks it has text to commit. This would result in a change event being
fired when the return key is pressed multiple times in a row.
We were also firing the beforeinput/input events twice for all return
key presses.
To fix this, this patch changes the input event target to signify if it
actually handled the return key. If not (i.e. for textarea elements),
only then do we insert the code point. We also must not fall through to
the generic key handler, to avoid the repeated input events.
We hold a raw pointer to the mouse selection target, which is a mixin-
style class inherited only by JS::Cell classes. By not visiting this
object, we sometime had a dangling reference to it after it had been
garbage collected.
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
