@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 can be disabled with the new `--quiet` option.
Printing every commit would give the user all the information of how to undo
this or where to `jj restore` from if they realize they need to after the
abandon.
