Use $separator at the start of entries in recent changes.

This patches modifies Flow to use $separator at the start of entries in recent
changes, which makes entries generated by Flow more consistent with those not
created by Flow.

Bug: T76170
Change-Id: I0662dee9bc7af7c357dd6da6a11caa8380eb0a6f
Merge "Use $separator at the start of entries in recent changes."