Fix HUNs re-showing after shade closes

Also fix HUNs not being pinned while scrolled:

Clear waiting HUNs and turn off throttling when reordering is not allowed

Bug: 342555873

Test: send delayed HUNs in shade/swipe-unlock lockscreen,
      wait until HUNs show up, swipe to close shade
      => HUNs do not re-show in floating pinned state

Test: send delayed HUNs, open shade with notifs
      => new HUNs show up at top of HUN section

Test: send delayed HUNs, open shade with notifs and scroll
      => HUN pinning while scrolled works fine

Test: HUN-to-shade transition works fine

Flag: com.android.systemui.notification_throttle_hun

Change-Id: I298e610aa7c60863d6ef9672c0b19e19b264e1a9