Add ACTION_KEYBOARD_LAYOUT_SETTINGS.

This CL adds ACTION_KEYBOARD_LAYOUT_SETTINGS so that IME developers can
navigate users to the settings to configure the hardware keyboard layout
as needed, as we have exposed ACTION_INPUT_METHOD_SETTINGS and
ACTION_INPUT_METHOD_SUBTYPE_SETTINGS.

Bug: 25752827
Change-Id: I8f371702904b3354043cd6d23fc9a8ff8be9b537