`mergeEdges` should merge individual edges as late as possible in a branch situation regardless of branch lengths

[giorgosera]

As discussed on Gitter I have this graph which does not satisfy my use case.

Specifically, I've set mergeEdges to true and as you can see the two rightmost edges are merging at a different level than the leftmost one. The desired result would be for all of them to merge at the bottom of the branch as seen in this other graph (for which I have removed the INTERACTIVE layering strategy).

If I set the mergeEdges to false then the edges are routed as expected but of course this doesn't generate the desired output.

Could we please have an option where the edges can merge as late as possible?