Improve color section loading

Make sure preset colors are loaded only once by keeping track of the
loading job and joining it.
Make the overflow option the same height as a selected option to avoid
a change in the section height when the options load.

Bug: 332749262
Test: atest WallpaperPickerTests
Test: Manually compared jank. See video in bug
Flag: N/A
Change-Id: I033aa8dde215fbe1cc610f279b6934a5b5340429