Support wallpaper on secondary displays.(7/N)

Expand the wallpaper color listener for multiple displays. This will
allow the launcher on the secondary display can also receive the
correct wallpaper color.

Bug: 115486823
Test: atest WallpaperManagerTest
Test: atest ActivityManagerMultiDisplayTests
Change-Id: I3d893537a8c606170b5641c9eb4683d09743d80c