Dangling line pairing refactoring

[olperr1]

Describe the current behavior

The code doing the dangling lines pairing when merging networks is hard to read (especially the TieLineUtil.findAndAssociateDanglingLines method) and to evolve.

Describe the expected behavior

Refactor the dangling lines pairing when merging networks to make it more maintainable.

TieLineUtil.findCandidateDanglingLines (introduced by #2740) can be called on both networks to merge in order to identify the dangling lines to pair.

Describe the motivation

No response

Extra Information

No response