SYSML2_ — Flows cannot connect ControlNodes

Allow flows to connect ControlNodes because, currently, this limitation makes it impossible to pass payloads from one ActionUsage to another ActionUsage if a DecisionNode is in between.
This issue is a showstopper for the UAF v2 development.

Update textual notation for control nodes

The abstract syntax actually allows control nodes to have parameters. These can be used as the source and target of flows from and to a control node. In particular, if these flows are succession flows, then the control nodes enforce the appropriate control semantics on the successions, with the flow through the nodes being handled in their bodies. This is the approached used, for example, in resolution SYSML2_-439 to issue SYSML2_-111 for the mapping of SysML v1 fork and join nodes to SysML v2.

Unfortunately, until now, the concrete syntax did not allow the declaration of parameters in control nodes, or anything else in their bodies other than annotations. This resolution corrects that by revising the textual notation grammar for control nodes. Updates to the graphical notation and flow-specific semantic modeling for control nodes are deferred to a future RTF.

The resolution also adds a constraint in the abstract syntax requiring that control nodes be composite, which is consistent with the textual notation and their semantics.