Complete the transitions among hub mode, idle mode, and low light mode.

Note that the transition from low light to idle mode requires
switching between dozing and dreaming states, which are asyncronous
operations that call into the PowerManager and Sandman. This CL
implements a temporay solution to wait for dozing state to finish before
starting dreaming, which will be removed once switched to the
SurfaceView implementation of the idle screen.

Video: https://drive.google.com/file/d/151FWbEJofzoV9Z-hLmgo0PzOwYly1-wm/view?usp=sharing&resourcekey=0-H6wtcD3wiV8PzEOnbBzQBg

Change-Id: I8fd2790544038630007b18b29abaea37acbf9399
Test: atest IdleHostViewControllerTest
Bug: 196108994