Tie line API improvement

[annetill]

Describe the current behavior

What we have to do now is:

Optional<TieLine> optionalTieLine = danglingLine.getTieLine();
if (optionalTieLine.isPresent()) {
       TieLine tieLine = optionalTieLine.get();
       DanglingLine otherSide = tieLine.getDanglingLine1() == danglingLine ? tieLine.getDanglingLine2() : tieLine.getDanglingLine1();

Describe the expected behavior

Add a dedicated method in the API that returns the optional other side dangling line.

Describe the motivation

No response

Extra Information

No response