popup window is closed with Xorg gnome-shell and ibus if its password entry is focued on

The original bug is https://github.com/ibus/ibus/issues/2002

When the password entry is focused in a popup window in firefox in GNOME xorg, 'set-content-type' signal is received in js/misc/ibusManager.js to set the GTK_INPUT_PURPOSE_PASSWORD. And gnome-shell calls KeyboardManager.holdKeyboard() and KeyboardManager.releaseKeyboard() in js/ui/status/keyboard.js and the popup window is always closed.

meta_display_freeze_keyboard() works for META_IS_BACKEND_X11() only.