Do not capture swipes in opposite direction.

This changelist updates the logic in BouncerSwipeTouchHandler to
validate the direction of the vertical swipe. Accepting swipes in the
opposite direction (such as down on a collapsed bouncer) can cause
lockscreen/shade ui locking up.

Test: atest BouncerSwipeTouchHandlerTest
Flag: ACONFIG com.android.systemui.dream_overlay_bouncer_swipe_direction_filtering DISABLED
Change-Id: I954fd8d61248319646539fa60c89fe728cf21f71