Use SDL_Start/StopTextInput() also with SDL2

Based on whether handleMouseGrab() in events.cpp sets
GRAB_ENABLETEXTINPUT or not.

Should prevent the issue that on macOS pressing a button for longer
while playing (as one does, e.g. to run forward) opens a popup menu
with alternative characters (like "è", "é", "ê", etc for "e")

neo/sys/glimp.cpp

@@ -1191,6 +1191,11 @@ void GLimp_GrabInput(int flags) {
 	SDL_ShowCursor( (flags & GRAB_HIDECURSOR) ? SDL_DISABLE : SDL_ENABLE );
 	SDL_SetRelativeMouseMode( (flags & GRAB_RELATIVEMOUSE) ? SDL_TRUE : SDL_FALSE );
 	SDL_SetWindowGrab( window, (flags & GRAB_GRABMOUSE) ? SDL_TRUE : SDL_FALSE );
+	if (flags & GRAB_ENABLETEXTINPUT) {
+		SDL_StartTextInput();
+	} else {
+		SDL_StopTextInput();
+	}
 #else
 	SDL_ShowCursor( (flags & GRAB_HIDECURSOR) ? SDL_DISABLE : SDL_ENABLE );
 	// ignore GRAB_GRABMOUSE, SDL1.2 doesn't support grabbing without relative mode