Let DragView use ActivityContext instead of Launcher

- Make DragView abstract and extended by LauncherDragView for the explicitly Launcher-specific parts.
- Some other methods like Utilities.getFullDrawable() now accept (Activity)Context rather than Launcher.

Test: Compiles and runs, manual drag and drop
Bug: 182981908
Change-Id: I77b7a2e48ce864dd711c3232217fdba4d60c546f
8 files changed