Add a getDirectionFromRange Method to ve.ce.Document

getDirectionFromRange returns the direction property of the ce nodes under
that range. That method is mostly useful to recognize the overall block
direction of a selection or fragment.

The method is currently used in the following locations:
* ve.ui.Toolbar onContextChange - as a means to recognize the current context's
  block direction for the icon directionality.
* ve.ui.MWExtensionInspector - if the selection is text and not an existing node
  the input directionality adjusts to the context direction.

Bug: 57421
Change-Id: Ifc01b8e5dc0a2fe39d221e59e452c5cfad709a2d
Merge "Add a getDirectionFromRange Method to ve.ce.Document"