Add local wallpaper color extraction to folder backgrounds.

- Starts listening to local wallpaper colors as soon as folder
  is positioned.
- The folder open animation already has a background color
  animator.
- For simplicity, folder open animation always starts
  first, and then we cancel its background color animator,
  and start a new animator to the extracted color.
- setAutoCancel would be handy here, but it does not work, will
  track in a separate bug.
- Since folders are reused, we clear our the color extractor on
  folder close.

Bug: 175329686
Test: multiple folders on rainbow background
      open each folder, ensure bg animates to proper color
Change-Id: Ie0f2c0632fa2361f7710ba247d74f882620dec16