Add bottom right chip to dream overlay to show glanceable hub

This is added temporarily behind a flag for UX testing purposes and is
not intended to be a proper, full implementation.

Chip can be moved to the bottom left, replacing the home controls
button, by changing the system setting
open_hub_chip_replace_home_controls to 1.

Bug: 339667383
Test: N/A
Flag: com.android.systemui.glanceable_hub_shortcut_button
Change-Id: I34ef11c5d764ca46aea074b14d19f2ac804e3941