[Security analysis] Report power transfer ratios in results

[sylvlecl]

• Do you want to request a feature or report a bug?

Feature.

• What is the current behavior?

Security analysis only report limit violations, it does not report power transfer ratios.

• What is the expected behavior?

Be able to retrieve power transfer ratios from the security analysis result.
Power transfer ratio of a contingency on branch B1 on another branch B2 is defined as the difference of active power on branch B1 between N situation and post-contingency situation divided by the active power on branch B2 in N situation.

The same concept can apply to currents.

Note that if we implement #1699, this issue might be considered irrelevant and left for implementation to the user ?

• What is the motivation / use case for changing the behavior?

We cannot efficiently compute power transfer ratios with the current API, since the only option is to run a loadflow for each contingency.

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

Power transfer ratios could be reported in PostContingencyResult class:

public class PostContingencyResult {
    private final Contingency contingency;
    private final LimitViolationsResult limitViolationsResult;
    private final List<PowerTransfer> 
    ...
}

public class PowerTransfer {
    private final String branchId;
    private final double ratio;
    private final double nSituationValue;
    private final double postContingencyValue;
}