[ContextMenu] Add ability to control

[benoitgrelard]

A few users have needed to control the ContextMenu in some scenarios (typically canvas based apps) so it would be good if we could provide a way to do so.

[mrudowski]

i think this approach is very handy - just a anchorPoint to work with onShapeContextMenu

[Andarist]

What kind of control are we talking about here? Just the open state? Or something else too? My use case is that I'd like to conditionally disable the context menu - which could be faked through open={isDisabled ? false : undefined} (as long as the component would handle switching between controlled and uncontrolled "modes" gracefully)