We delegate page up / page down actions to the browser. However, we don't let the browser scroll the underlying `<textarea>` - the framework handles scrolling, so page up/down don't end up doing anything. Since the framework handles scrolling for text inputs and textareas, we should let it also handle the actions for `page up`, `page down`, `home`, `end`, and their modifiers. 

fixes https://github.com/flutter/flutter/issues/121867