Add new content handling methods and implementation

Bug: 347235611
Test: manual testing with flag enabled and disabled
Test: CTS tests to be added with b/373596341
Flag: android.app.live_wallpaper_content_handling
API-Coverage-Bug: 373596341
Change-Id: I6f79b5ed85be8ba0bc52021e8ddac274d47d4273
12 files changed