Otherwise the description set by -m would differ from the one set by editor.
This fixes test_describe() which says "make no changes", but previously "\n"
would be added by the second "jj describe".
As you can see, almost all hashes change in CLI tests. This means in-flight
PRs will need to be rebased to update insta snapshots.
Description text could be normalized by CommitBuilder, but the caller would
have to normalize it beforehand to compare with the current description, so
we would need an explicit function anyway. Another idea is to add a newtype
that represents a normalized description, and make CommitBuilder require it.
Commit::description() will return &Description in place of &str to ensure
that commit.description() == raw_str wouldn't compile.
Git CLI provides --cleanup=<mode> option to switch normalization rules, but
I don't think we'll need such feature.
