With this CL, LatinIME starts using
InputMethodManager#shouldOfferSwitchingToNextInputMethod when
available and API level is higher than 19 (KitKat).

Note that relevant settings of LatinIME will be ignored if
InputMethodManager#shouldOfferSwitchingToNextInputMethod is
considered to be available at the moment. We will revisit
here to reorganize the user visible settings before the
new global IME switching mechanism becomes publicly
available.

BUG: 12965588
Change-Id: I0188fa56cba8e983c61cef3ae3400a0e3821f718