graph: sort parents from farthest to closest

[zummenix]

This is a follow up of #3048

Please note that I don't fully understand what I'm doing here, bear with me :)

Currently, as I understand, the edges for children with multiple parents are "drawn" in exact order they appear in the graph, which leads to cases like this:

@   merge
├─╮
◉ │  fix
├─╯
◉  initial
│
◉

First parent of merge is fix and second is initial.

More visually appealing graph would be (in my opinion) when merge has first parent initial (oldest/farthest) and second parent fix (newest/closest). If we sort parents by their position we get:

@    merge
├─╮
│ ◉  fix
├─╯
◉  initial
│
◉

I've added the change in RevsetGraphIterator (I'm not sure if this is the right place) and two tests to check that the order of commits in a merge does not matter. The other changes are test snapshots (which I've checked only briefly).

I'd like to hear your feedback.

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[zummenix]

I've looked into several repos with heavy branching and came to conclusion that this solution is wrong. Closing