Fix app staying in drag resizing when undocking

When dismissing the docked stack, the fullscreen stack stayed in drag
resize mode because it got a relayout, but because the bounds didn't
change (it switches to the fullscreen layout a bit earlier) it never
called WM.relayoutWindow, so it stayed in drag resize mode indefinitely.

To fix this, introduce forceRelayout in Window.resized(), which makes
sure the client always calls relayoutWindow. Set this to true whenever
drag resizing is changing.

For some very weird reason this also broke that home button was not
responding anymore.

Bug: 26806532
Change-Id: I4b39c1c419a166aa7093c31226f2a4915f642328