Limit task bounds to stable bounds if resizing beyond the stable bounds.

Previously, the repeated rounding down of a float to an int when
resizing leaves a few dp gap when the user resizes beyond the stable
bounds.

Fix: 327433091
Test: manual resizing using touch and cursor, atest WMShellUnitTests:DragPositioningCallbackUtilityTest
Flag: EXEMPT bug fix
Change-Id: I4129322ffe97e3c3617b49e3e6c65e5bc151e4d7