This doesn't change anything, we just pin down the selection behavior
around conflicts; we are going to change that behavior, and these tests
will make it obvious how when they change in the next commit.
I'm not a skilled UI designer, so I suspect there may be even better
options, but it's definitely already better than the raw ASCII "---" we
had before.
Put the line only at the beginning because it looks bad if the line
after the label is misaligned when labels don't have the same width
(e.g. "Remote" vs. "Local" in the divergence view).
It is useful to see if the conflicted commit was a "pick" or an "edit". What's
more, we're about to add support for showing cherry-picks and reverts, and
seeing that a conflicted commit was a revert is important because its diff is
backwards compared to the diff of the conflicting files in the Files panel.
When stopping in a rebase because of a conflict, it is nice to see the commit
that git is trying to apply. Create a fake todo entry labelled "conflict" for
this, and show the "<-- YOU ARE HERE ---" string for that one (in red) instead
of for the real current head.
