Get PiP state from Shell in EdgeBackGestureHandler

We use to rely on the onActivityPinned and onActivityUnpinned callbacks
from Window Manager in EdgeBackGestureHandler to determine the current
PiP state and it will always be reset to false when
EdgeBackGestureHandler is being re-created, for instance, as a result of
folded state change.

Deprecated also the Pip#setPinnedStackAnimationListener interface method
since it's not in use and it may cause confusions over
IPip#setPinnedStackAnimationListener.

Bug: 174702196
Bug: 198651351
Test: stash in unfolded state -> fold -> drag to unstash \
      stash in folded state -> unfold -> drag to unstash
Test: atest WMShellUnitTests:PipControllerTest
Change-Id: Id874056415011ee8a55dadcd4ec6af6e1b568092