The Control#getLocation() and Control#setLocation(...) operations
currently claim to always work (i.e., yield reasonable values or
actually change the location). This specification is incorrect when
executing these methods in shells on a platform that uses the Wayland
protocol. Since there is currently no fix to make the implementation
fulfill the specification, this adds an according warning to the
specification in order to avoid that clients rely on the specification
to be fulfilled.

Contributes to
https://github.com/eclipse-platform/eclipse.platform.swt/issues/790