SYSML2_ — Graphical BNF production proxy should be contextualized

proxy refers to proxy-label should be sq-proxy-label
The BNF attempted to reuse the proxy graphics and productions across all three contexts where a proxy may appear (lifeline, ports, and parameters), but all these need to be replaced by proxy graphics specific to each context, including connector line segments above and below, or left and right, in each specific graphic context where a proxy dot may appear.