Seems "keydown" is better than "keypress" for catching Ctrl-W (to close a tab),  refs #16585 !strict.
Update varioius widgets to use native keydown event and evt.keyCode rather than synthetic keypress event and evt.charOrCode.   Didn't touch the code in _TextBoxMixin that calls this._onInput() with a homegrown synthetic event though.

Refs #16585 !strict.