Fancy animation for quick affordance option picker

Building on the companion WallpaperPicker2, this CL achieves a refactor
that allows the UI to actually animate user selection of quick
affordance items.

Part of this CL is a refactor that extracts out an "option item
framework" out into the WallpaperPicker2 code repository (please see the
other CL for thate).

Another part of this CL is a heavy refactor of
KeyguardQuickAffordancePickerViewModel which is the main view-model for
the "shortcuts" full-screen experience. Namely, we had to change it to
emit a stable list of option items (one for each lock screen shortcut)
where the _contents_ of it can change (namely, isSelected, onSelected
have both become flows). This required some careful restructuring of the
logic that populate the quickAffordances flow in that class.

Fix: 266116562
Test: existing view-model integration test updated to match new field
types, still passes without logical changes to the test
Test: manually verified the correctness of the UI in Walpaper & style >
Shortcuts
Test: manually verified animations: they do not happen when switching
tabs, they do not happen on initial load. They do happen when I select a
new affordance (both on the newly-selected one and the
previously-selected one).

Change-Id: I985afdfbbc72d0b98859df3378f2c90d2397e7d4