log: emit working-copy branch first if included in the revset

[yuja]

Checklist

If applicable:

• [x] 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)
• [x] I have added tests to cover my changes

[tim-janik]

Wow, live editing with jj-fzf works much better with this change applied when describing commits not on the working copy. The one thing left to wish for is stabilizing the order of siblings, but swapping sibling branches not related to the working copy is triggered less frequently than anything involving the working copy:

⮞ jj log
@  kwn
│ ○  kzw D
├─╯
│ ○  oll C
├─╯
○  xpx B
○  soq A
⮞ jj desc -m C2 -r 'description(exact:"C\n")' && jj log
@  kwn
│ ○  oll C2
├─╯
│ ○  kzw D
├─╯
○  xpx B
○  soq A

[yuja]

⮞ jj log
@  kwn
│ ○  kzw D
├─╯
│ ○  oll C
├─╯
○  xpx B
○  soq A
⮞ jj desc -m C2 -r 'description(exact:"C\n")' && jj log
@  kwn
│ ○  oll C2
├─╯
│ ○  kzw D
├─╯
○  xpx B
○  soq A

This wouldn't get stable order based on generation number either. We would need a weird tie-breaking rule such as heads are sorted by change ID, not by timestamp.

I think a UI will have to retain some state to avoid node reordering. For example, a set of head change ids can be queried first, then pass it to jj log --config-toml=prioritized_branches=[...] or something to enforce the order.