Polishing thresholds and reattaching.

We increase the magnetic detach and attach thresholds to allow more
swiping room. We also atract neighbors and restore magnetic pull forces
when the notification crosses the attach threshold. For better motion,
detachment and attachment now query the current gesture velocity.

Test: manual. Verified that attachment restores magnetic pulling and
  attracts neighbors. Tested at different swipe velocities.
Flag: com.android.systemui.magnetic_notification_swipes
Bug: 405450400

Change-Id: I70e7af5a6c42b652e3cf3107a8181f63bf9f8ae0