Allow dragging through the status bar on split-screen tasks

Changes the drag through the status bar event handling so that drag
is allowed when the task is in multi-window mode instead of just
fullscreen. Tasks in split (when desktop mode is enabled) have a
window decoration with a caption just like fullscreen tasks, so they
need to be draggable too.

Bug: 285395534
Test: with desktop mode enabled, put two apps in split, drag the
handle bar and verify it responds to touch and is able to be dragged
into freeform.

Change-Id: Ia92d25e10d890c9d6c875a202d16da56eb48d762