[HID] Enable Keyboard Passthru

Thanks Adrian for figuring out missing XINPUT_KEYSTROKE_VALIDUNICODE flag.
Thanks Clippy95 for figuring out shift and capslock

src/xenia/hid/sdl/sdl_input_driver.cc

@@ -288,7 +288,9 @@ X_RESULT SDLInputDriver::GetKeystroke(uint32_t users, uint32_t flags,
   if (!out_keystroke) {
     return X_ERROR_BAD_ARGUMENTS;
   }
-
+  if ((flags & XINPUT_FLAG_KEYBOARD) != 0) {
+    return X_ERROR_INVALID_PARAMETER;
+  }
   // The order of this list is also the order in which events are send if
   // multiple buttons change at once.
   static_assert(sizeof(X_INPUT_GAMEPAD::buttons) == 2);