Show unlock prompt when user interacts with the hub

This change also addresses an existing issue where tapping on the bottom
of the hub doesn't trigger customization or log the user interaction to
bump the screen timeout. This is because the hub composable no longer
takes up the entire screen, but is constrained to the lock icon. This
change therefore moves the touch handling logic out of the hub
composable and into the parent, so it can intercept touches across the
entire screen.

The widget selection logic is maintained in the hub for now to minimize
any behavior changes. In the future, the widget selection logic should
be moved to the actual widget views themselves.

Fixes: 340519071
Test: flashed device and verified long pressing on any blank space will
trigger customize prompt. Also, long pressing on a widget will trigger
customize prompt and pre-select that widget. Tapping on any blank space
will also trigger the unlock prompt now.
Flag: com.android.systemui.communal_hub

Change-Id: I1784cfc4c7bcead1efa8fc82e91a7d0e0f43e41d