Replace DragView bitmap with drawable

This is a preliminary work for local color extraction. In order to
apply local colors extracted from wallpaper to AppWidgetHostView
during drag, we need to hold a reference of the dragging
AppWidgetHostView.

In this CL, the following changes are made:
1. Instead of using bitmap image directly for icons, folders, shortcuts,
   legacy widget drawable preview, a BitmapDrawable wrapper is
    introduced.
2. Introduce a WidgetHostViewDraggableDrawable which draws
   LauncherAppWidgetHostView directly to canvas. No more bitmap
   generation overhead.
3. Remove drag outline from the drag logic because this will be replaced
   by a new grid color hint UI: https://screenshot.googleplex.com/7jBEVeuxFecFKKT.png

Test: Add: add widgets, shortcuts from widgets tray.
           add icons from all apps.
           create folder.
      Drag: drag existing widgets, shortcuts, folders and icons around

Bug: 182282587
Change-Id: Ia45ff756ea5bb80cf0761f0727a9453d50c204c0