SYSML2 — Need to complete and align flow and message notations in GBNF

The graphical notation lacks clear differentiation between the various types of flows in the language: flow, succession flows, and message flow (see also SYSML2-59).
In addition, the BNF was overly restrictive and did not allow flow connections on structural diagrams, except for flows on connections.
Flows on connections also need to include messages and succession flows.
It needs to be corrected in the BNF in the relevant clauses
8.2.3.9 - Occurrences (SD notation)
8.2.3.13 - Connections
8.2.3.14 - Interfaces
8.2.3.16 - Actions