Use Meta+Space for hard-keyboard layout switching

Currently we are not quite ready to have a system-level shortcut to
rotate IME language.  Until we become ready to do so, let's use
Meta+Space for hardware keyboard layout switching.

Fix: 79150878
Test: Manually tested as follows.
 1. Connect a hardware keyboard.
 2. Enable multiple hardware keyboard layouts.
 3. Make sure the hardware keyboard layout switches to the next one
    with Meta+Space.
 4. Make sure the hardware keyboard layout switches to the next one
    with Ctrl+Space.
 5. Make sure the hardware keyboard layout switches to the previous
    one with Shift+Ctrl+Space.
 6. Make sure the hardware keyboard layout switches to the previous
    one with Shift+Meta+Space.
Change-Id: Ife8a7100ec52792f4c42af2aa99298687c9af457