cursor: combine two variables relating to frame-context

cursor: combine two variables relating to frame-context

Mouse bindings, unlike key bindings, are made within contexts which
represent what was clicked/dragged.  The context 'Frame' refers to the
entire window frame including both the window decorations (if any) and the
client window itself. It is typically used for alti + left/right click to
move/resize the window.

'Frame' is a special case in that when a button is bound in this
context, the action will not be forwarded to the client, which is what
we describe with the 'consumed_by_frame_context' variable.