PiP: Consider stash state when calculating snap fraction.

If the PiP is stashed and something causes it to move (such as, screen
rotation or unexpand animations after timeout), we calculate its current
snap fraction, get the new bounds and movement bounds, and re-apply the
snap fraction. However during the snap fraction calculation, it assumes
that PiP bounds is within the movement bounds, which is not true when
PiP is stashed. So take this into consideration when doing the math.

This also changes the stashed status to reflect more than just yes/no -
but rather NONE/LEFT/RIGHT.

Bug: 165793553
Test: Stash PIP while menu is showing, and wait for timeout
Test: Stash PIP, rotate the device, see that snap fraction is persisted
Change-Id: Ib4eda44b7f280362b52609e4092dd4231ac8f04c