@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.
