Reset the IME if requested by the app.

Specifically, reset the KeyboardState to the main Alphabet layout in
LatinIME.onStartInputViewInternal() if a keyboard layout set doesn't get
reloaded in the method.

Please note TextView.setText() calls up resetInput(), then the IME should
reset with it.

bug: 7482086

Note that bug: 6851364 needs to be revisited.

Change-Id: I5d448c10963d3dd952dd13cb587085ec7b014e69