Improve TransitionUsage to improve control of succession of action

[adaussy]

TransitionUsage are used to define successions between different kind of actions.

In the following textual example, the outgoing successions of the DecisionNode are materialized using TransitionUsage.

action a0 {
    private import ScalarValues::*;
    action a1;
    action a2;
    action a3;
    action a4;
   
    attribute attr1 : Real;
    first a0 then d1;
    decide d1;
        if x >= 2 then a1; //<- Here
        if x >= 1 and x < 2 then a3; //<- And here
        else a4;  
}

This issue aims to provide:

• Valid import/export capabilities for TransitionUsage in the context of succession of Actions
• Improve diagram to be able represent such TransitionUsage in the GeneralView diagram

[AxelRICHARD]

That's two distinct issues here.
Could you please create a separate issue for the Improve diagram to be able represent such TransitionUsage in the GeneralView diagram?
For the next issues, please keep in mind that we try to have one problem/case per issue.