fix the flickr from HUN to quick settings

When the HUN show the IME, the user start to drag the HUN and the
target scroll value use getTopPadding() to count. Actually, in that
moment, HUN show on mHeadsUpInset position. i.e. mHeadsUpInset is
appropriate to be used by HUN in that moment.

The root cause is that ExpandableNotificationRow's headsUpIsVisible
never set to be true when the user move down and up the HUN. The
following NotificationStackScrollLayout.mChildrenUpdater will not
update ExpandableNotificationRow.mustStayOnScreen to be false.

The user move down or up the HUN which has the input field with IME
showing. The user already doesn't care these HUNs so all of HUNs
should unpinned and set mustStayOnScreen to be false. Any of
user's operations that trigger unpined all of HUNs should set
mustStayOnScreen too.

Change-Id: If68c11a889805100feeea0fa7d983481fad01161
Fixes: 111244087
Fixes: 110774347
Test: manual test