Move wallpaper display logic in WallpaperDisplayHelper

Part of the WallpaperManagerService refactor.

This CL also moves the class DisplayConnector out of WallpaperConnection.

Test: atest CtsWallpaperTestCases
Test: atest FrameworksMockingServicesTests:WallpaperManagerServiceTests
Bug: 264637309
Change-Id: I9e8ca8c7237ed414193803b36c7e604d8d615e6b
3 files changed