Better overflow button

Overflow button as BadgedImageView
- BadgedImageView uses launcher’s icon factory to render overflow icon, which fixes the size and space inconsistencies between real bubbles and a bare ImageView
- BadgedImageView gives us access to the existing dot drawing logic, which we can later use to draw a dot on overflow button when overflow bubbles get updates
- Replace Bubble with BubbleViewProvider inside BadgedImageView so that BadgedImageView can access BubbleOverflow’s dot info

UI polish
- Set margins for overflow bubbles
- Set padding for overflow empty state
- Set overflow button and dot color to accent color from theme
- Render overflow button based on theme and dark mode; update on change

Bug: 149146374
Bug: 148878911
Test: manual - overflow button shape, icon color updates on theme change
Test: manual - overflow button color updates on dark mode change
Test: manual - overflow UI looks like mocks (specs not final)
Test: atest SystemUITests
Change-Id: I3d8829d56bce5c80936698a038438aff6db42d0f