Connected sections for wallpaper and colors (2/3).

This is a side-by-side layout for the color and wallpaper quick switcher sections on the main/landing screen of wallpaper picker.

Bug: 265837104
Test: manually verified layout on large screens in landscape and
portrait mode, hand-helds in portrait mode - both with left-to-right
(English) and right-to-left (Hebrew) setups

Change-Id: I5e03344ba8a365803e4df3a031ce0ec1f2f1b862