SYSML21 — Accept action payload parameter has the wrong direction

In 8.2.2.17.4 Send and Accept Action Usages, the payload parameter of an AcceptActionUsage is parsed as being owned by a ParameterMembership. This requires that the parameter have the direction in (see 8.3.4.6.4). However, the payload parameter of the base library definition Actions::Action has the direction inout. While it is valid to redefine an inout parameter with an in parameter, it is generally the output payload value that is desired from an accept action. Therefore, the payload parameter of an AcceptActionUsage should also have direction inout.