[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/xinput/xinput_input_driver.cc

@@ -200,6 +200,9 @@ X_RESULT XInputInputDriver::GetKeystroke(uint32_t user_index, uint32_t flags,
   // flags is reserved on desktop.
   DWORD result;
 
+  if ((flags & XINPUT_FLAG_KEYBOARD) != 0) {
+    return X_ERROR_INVALID_PARAMETER;
+  }
   // XInputGetKeystroke on Windows has a bug where it will return
   // ERROR_SUCCESS (0) even if the device is not connected:
   // https://stackoverflow.com/questions/23669238/xinputgetkeystroke-returning-error-success-while-controller-is-unplugged