Clarify language around unlisted and direct posts

[trwnh]

• Renames "Unlisted" to "Not in public timelines"
• Emphasize "mentioned people only" applies to the current post

[trwnh]

@ykzts Changed all the components and source files corresponding to the changed messages, thank you ^_^;

[ClearlyClaire]

Unlisted also opts out of trending

[trwnh]

I think in the long term "unlisted" should be replaced by toot:discoverable flag being applied to statuses and not just profiles, and maybe making it a separate per-post toggle for discoverability, but so long as we have current privacy scopes, maybe calling it "Semi-Public" isn't so bad. In any case, we can't really control what other implementations do, and it doesn't feel worth mentioning non-self-reply-filtering from timelines either, as that could change. So what about the following?

"Semi-Public"

"Visible to anyone on your profile and in home timelines[, but not in public timelines, hashtags, or trends]"

I'm not sure if the second half is strictly necessary or implied by the first half, or if it could be replaced by the word "only". I'm inclined to think it might be. We already have a hint banner that appears when someone tries to use a hashtag in an unlisted post.

[github-actions[bot]]

This pull request has merge conflicts that must be resolved before it can be merged.

[mjankowski]

Closing due to no activity in ~1 year, merge conflicts, and lack of consensus around the "unlisted" specific changes.

If you want to push the rest forward, can you rebase and reopen with just the non-unlisted-related changes in this PR?