Update Dispatch_Trigger to list features

[jjhugues]

The definition of Dispatch_Trigger must be updated to list feature Rationale: we must also allow incoming calls to subprogram access

As a consequence, we need the following consistency checks

• list of features that are referenced belong to the component the property applies to (to avoid listing features of another unrelated component)
• list of features are "in", i.e. in event (data) port or provides subprogram access. Must discuss the case of data port
• can dispatch_trigger be set for background and periodic threads? what is the semantics?
  • background may self-suspend and behave as aperiodic, but this would be a breach in their dispatching contracts ..

[jjhugues]

Consistency rule added in A.2, 5.4.2 defined trigger features, no need to go further than pointing to the definition