Rename 'draw' or 'drawcall' to action

* There's not a good accepted terminology for this kind of event, and for
  historical reasons 'drawcall' has been the accepted term, even though
  that can be quite confusing when a dispatch or a copy is a 'drawcall'.
* This is particularly highlighted by the event browser filters where
  $draw() includes draws and dispatches, but $dispatch() only includes
  dispatches, it's hard to intuitively understand why $draw() matches all
  of these calls.
* As a result we've defined the term 'action' to cover these types of
  events in the same way that we defined 'event' in the first place to
  mean a single atomic API call.

docs/python_api/examples/renderdoc_intro.py

@@ -23,7 +23,7 @@ if status != rd.ReplayStatus.Succeeded:
     raise RuntimeError("Couldn't initialise replay: " + str(status))
 
 # Now we can use the controller!
-print("%d top-level drawcalls" % len(controller.GetDrawcalls()))
+print("%d top-level actions" % len(controller.GetRootActions()))
 
 controller.Shutdown()