Let's acknowledge everyone's contributions by replacing "Google LLC"
in the copyright header by "The Jujutsu Authors". If I understand
correctly, it won't have any legal effect, but maybe it still helps
reduce concerns from contributors (though I haven't heard any
concerns).
Google employees can read about Google's policy at
go/releasing/contributions#copyright.
This makes the tests more hermetic, even though I don't think the
default values (taken from `whoami`) can break any tests (then we
would have already seen them break). Now we just need to make the
operation log's timestamps predictable and then we can start using
operation IDs in snapshot tests.
We currently get the hostname and username from the `whoami` crate. We
do that in lib crate, without giving the caller a way to override
them. That seems wrong since it might be used in a server and
performing operations on behalf of some other user. This commit makes
the hostname and username configurable, so the calling crate can pass
them in. If they have not been passed in, we still default to the
values from the `whoami` crate.
It's useful for testing to be able to specify some operation that's
not the latest one.
I didn't update the changelog because this feature is mostly for
testing.
