SYSML2 — Textual notation BNF for TriggerExpression is wrong

Time and change triggers for an accept action are supposed to be parsed as a TriggerInvocationExpression with a single argument: for a time trigger, the argument is a duration or time instant, while for a change trigger it is a boolean expression. However, the textual notation BNF for TriggerExpression in 8.2.2.16.4 is not properly parsing the textual notation as an invocation with arguments. As a result, the intended argument expression for the TriggerInocationExpression will not actually be recognized as an argument of the invocation.

Update TriggerExpression BNF

Update the TriggerExpression BNF to properly synthesize parameters for the TriggerInvocationExpression.