Put the "floating" in ENABLE_FLOATING_SEARCH_BAR.

This means adding the search view to the drag layer, so it can
persist and animate across Launcher states (i.e. Home, All Apps,
Overview, Overview from App).

Some high level things:
 - LauncherState now has a flag indicating if the floating
   search bar should be visible, as well as a method indicating
   how high it should rest when the keyboard is not showing. By
   default the height is set negative if the flag is not present,
   so the search bar will rest off screen in that state.
 - LauncherState also has a new method indicating if the search
   bar should show as a pill when not focused. Currently this is
   done in phone portrait mode in all apps and overview.
 - SearchUiManager now has a method for gestures to hint that
   the search bar will be focused or unfocused soon, e.g. for
   the app -> overview case, we hint that it will be focused
   when crossing the threshold, and unfocused if retracting.
   This allows the search bar to animate during the gesture
   and take or release focus after the state change completes.
 - AllAppsTransitionController lets the apps panel translate in
   from the bottom of the screen, for example when coming from
   an app and we don't want to pop it in halfway up the screen.
   Instead it can slide in gracefully from behind the keyboard
   and floating search bar.
 - KeyboardInsetAnimationCallback can now notify listeners of
   keyboard alpha changes during controlled animations. And
   StateAnimationConfig has a new animation type to control
   the keyboard alpha during the all apps transition.
 - This new ANIM_ALL_APPS_KEYBOARD_FADE is used to pop the
   keyboard in at the threshold for going from an app to all apps.
   Note that its position moves linearly before this, so the
   search bar starts moving up accordingly before the keyboard
   alpha is non-0.

Fix: 266761289
Fix: 268845147
Fix: 267683921
Fix: 265849321
Fix: 266446733
Fix: 269301440
Bug: 275635606
Bug: 259619990
Bug: 261866704
Test: Manual with all the state transitions on phone and tablet
(also folding/unfolding foldable).
Flag: ENABLE_FLOATING_SEARCH_BAR, ENABLE_ALL_APPS_FROM_OVERVIEW
(latter just for the background app interpolator changes).

Change-Id: I6f06552e95747348a62260279626cf407bf145b0