[flexiglass] Add Snoozeable HUN Placeholder and HUN touch handling

Creates a variant of HeadsUpNotificationSpace that can be swiped up off the screen. Currently, doing so triggers most of the side effects as in legacy, but not all (to be validated in a follow-up CL). In addition, when flexiglass is on, NSSLC creates an instance of HeadsUpTouchHelper with an empty impl for the NPVC interface, so that we can reuse the touch tracking by calling it in NSSLC's touch handling methods. The side effects that have been left unflagged in HeadsUpTouchHelper didn't seem to be broken, but it might be better to move them elsewhere later.

Bug: 340514839
Test: Verified HeadsUpTouchHelper internal state is updated correctly during swipes on HUNs via logging
Test: Verified NSSL dragging state is updated correctly via logging
Test: Verified dragging and flinging HUN placeholder over Gone scene upwards moves it off screen
Test: Verified dragging and flinging HUN placeholder downwards opens Shade scene
Test: Verified letting go of HUN placeholder before reaching thresholds animates it back to pinned position
Test: Verified changing directions while swiping HUN placeholder works as expected
Flag: com.android.systemui.scene_container
Change-Id: I62631f1f9dc8ff1e52cac2366ed310a6b3f0cc1f