keyboard: Do not call KeyboardManager.holdKeyboard() with set-content-type
cherry-pick of the following to 3.30:
When gnome-shell receives the signal of 'set-content-type' from ibus, gnome-shell calls KeyboardManager.holdKeyboard() and KeyboardManager.releaseKeyboard() and the functions change the current input focus in GNOME Xorg and it could result in closing a popup window which has a password entry by focusing on the entry. The solution is to stop to call the APIs on 'set-content-type' signal.
(cherry picked from commit 551e8278)