Adding some trace tags around system drag and drop

- This CL adds some trace points to better understand drag and drop
  performance.  In particular it adds
  - Client side: startDragAndDrop (trace points for drag shadow drawing,
    call to WM), handleDragEvent (trace points for drag event handling
    for non-LOCATION events)
  - WM side: DragDropController (trace points for dispatching of START,
    DROP, END, and notifying unhandled drops)
  - Shell side: GlobalDragListener (trace points for unhandled drop)

Bug: 308749691
Test: Take a perfetto trace w/ a global drag
Change-Id: Ib9abd414fe67f20ffc3c9dfe261e87ccd8dda766