On "jj checkout", description of the working-copy commit is empty, and the
working-copy parent provides more information. It might be a bit verbose to
print parent summary on every history rewriting, but I think that's okay.
This follows up on 5c703aeb0397b560a383bdd57a87235834074b64.
The only reason for this change is that, subjectively, the result looks better to me. I'm not sure why, but I couldn't get used to the old symbol in spite of its seeming reasonableness. It felt really bold and heavy.
If people agree, we can wait until we need to update the screenshots for some other reason before merging this. Sorry I didn't figure this out while the discussion about the referenced commit was going on.
I'm not 100% certain how many fonts support each symbol. Please try it out and let me know if it doesn't work for you.
Compare after:

and before:

@joyously found `o` confusing because it's a valid change id prefix. I
don't have much preference, but `●` seems fine. The "ascii",
"ascii-large", and "legacy" graph styles still use "o".
I didn't change `@` since it seems useful to have that match the
symbol used on the CLI. I don't think we want to have users do
something like `jj co ◎-`.
This eliminates ambiguous parsing between "func()" and "expr ()".
I chose "++" as template concatenation operator in case we want to add
bit-wise negate operator. It's also easier to find/replace than "~".
This allows us to use "if(description,)" to test empty description. And
I think this change is unavoidable if we want to add support for commit
template.
The `indexmap` crate is used to make `duplicate`'s output have a sane order,
making it easier to test.
It's also used later to remove duplicate revisions in the `abandon` command.
Fixes https://github.com/martinvonz/jj/issues/1050
Thanks to Martin for suggesting the exact fix.
The tests go into the new tests/test_duplicate_command.rs, which will be
expanded shortly with other tests depending on this bugfix.