Allow hub to be closed using full canvas swipe

Currently, the hub can only be closed by swiping on the left edge. This
change allows the hub to be closed by swiping anywhere on the screen.

Fixes: 346330753
Test: verified on hub with < 6 widgets where there is no scrolling
Test: verified on hub with > 6 widgets where the grid scrolls
Flag: com.android.systemui.communal_hub
Change-Id: Id0559242301527bd7531e4af3b9a953754c1d04d