Support event variables in transition expressions

[MarcoLm993]

When writing an expression that refers to an event param, often the type of that param is not known beforehand and hence we cannot determine the expression resulting type.

The current workaround is to use additional (local) variables, that store the value before evaluating that in the expression, but it is far from being an optimal solution.

One approach we could investigate within this issue is the following:

• Determine all events senders in the model, and store the parameters -> type association before starting the conversion.
• Once that is done, use the information in the scxml to jani conversion, without the need of using support variables.

This falls in the "refactoring of AS2FM" category, most likely...

[MarcoLm993]

Some more food for thoughts: convince-project/data-model@25b118f

[ct2034]

e.g.

        <transition event="a" target="current">
            <assign location="successful_transition" expr="edges_end[a_edge_location[_event.data.id]] == edges_start[_event.data.edge_goal]" />
            <assign location="a_edge_location[_event.data.id]" expr="_event.data.edge_goal" />
        </transition>