Change the way we decide whether we want to show on-screen keyboard by
not only paying attention to modifiers, but also keeping track whether
the key sequence started in the right state.

We are still misfiring if user presses a non-modifier key and then our
modifier hot-key, but such sequence is unlikely. Given the fact that we
do not want to store too much state I believe this deficiency is
acceptable.

Bug: 25087681
Bug: 24142161

Change-Id: I1a6b5e8e903c27a87134a6c9a7cd474a0607d5c8
(cherry picked from commit 7c513455918a52bd28c1c8181cb2880db0973b4b)

Out of the box, we want Alt-Left to toggle Emojis, while Alt-Right
toggles the shifted symbols layout.

Bug: 23954008
Bug: 24369173

Change-Id: I93dd66fb469e5d0a831359ff3a786fe68e1d73ea
(cherry picked from commit 411841b374aa04e333ea5a438dfd539f49ec589a)

Bug 23900149.

Change-Id: Iff8a3892bb88f82736e5fa680c38d98cda4d2777
(cherry picked from commit e1641395e30de7b53b06fc5c820ea83bf04b3aad)

When the LatinIME does not have an active InputConnection, it will not try
to toggle the Emoji keyboard.

Bug 19513415.

Change-Id: I31f928cd7db1cddd771c548cd3dc42f8af64d0e2

This CL also adds a settings option to enable/disable an Emoji-ALT
physical key.

Bug: 18122464
Change-Id: Iee1d97efec979a902b0492071d5e511ca1792ff0