Snap Slider on finish editing.

This creates a behaviour when
 - Volume Dialog snaps to minimum value when released so that the slider
   matches the icon state;
 - Volume Panel always snaps to immediate state;

Flag: com.android.systemui.volume_redesign
Fixes: 415246619
Test: atest VolumeDialogScreenshotTest
Test: atest VolumePanelScreenshotTest
Test: manual on foldable. Adjust volume using slider in Volume Panel and
Volume Dialog.

Change-Id: I377de7700b32bd9a481945d7b8415c43a2bb271c