I handle command+C and command+V shortcuts for copy/paste from clipboard using
SDL_GetClipboardText/SDL_SetClipboardText. But on iOS command+V shortcut is
also handled by system, so that I also get textinput event with that clipboard
text. And thus the application gets this clipboard text twice (from
SDL_GetClipboardText and from textinput event).
I assume that intended behavior is that command+V shouldn't generate textinput
events. At least as far as I know ctrl+V on other platforms does nothing. This
commit disables paste action for UITextField, so that textinput event isn't
generated anymore.