Notify task freeform constrains change to system UI (5/N)

This patch introduces freeform constraints, including the resize mode
and the minimal size to TaskDescription of TaskRecord. This will be
used to draw the resizing bounds before actually get the resizing done
by the WM. It will provide a better support for resizing strategies
including guide-view and background color fill.

Bug: 113253712
Bug: 122726344
Bug: 143496800
Test: go/wm-smoke
Test: Manually registered a listener from system UI and the event is
      correctly received.

Change-Id: I430c165cfb52ae4135c8d9328f682b8d305d0302