Some key events to build a wallpaper which can support multiple display. - The rendering or event handler of each engine must be independent. - Set supportsMultipleDisplays attribute to true. - Use Engine#getDisplayContext to load resource if needed. Bug: 129696884 Test: launch wallpaper and check on multi display. Change-Id: I3c60caba921e0af3d5f681ed318a543328e3375a