R1:0569919eab54

Fix some visibility issues with inline comments in Diffusion

Summary:
Fixes T10519. Two issues:

First, the acting user wasn't explicitly included in the mail. This usually didn't matter, but could matter if you unsubscribed and then interacted.

Second, we had some logic which tried to hide redundant "added inline comment" transactions, but could hide them inappropriately. In particular, if another action (like a subscribe) was present in the same group, we could hide the inlines because of that other…