Renames CSS rule that styles Zulip UI icons in the help center
so that it makes sense to use it regardless of whether we are
documenting a mobile or desktop/web feature.
- Documents the new contextually-aware button since the instructions
now differ depending on whether you're currently in a direct message
view or not.
- Simplifies the new topic instructions by combining the first two
tabs into a single web/desktop tab, with an optional step 2 to
change the destination stream.
Fixes#27159.
With the private messages -> direct messages migration, we should
rename the "Starting a new private thread" help center article.
- Renames article to "Starting a new direct message"
- Updates relevant section in /help/getting-started-with-zulip
- Fixes typo in /help/send-group-dm
- Updates file names and adds URL redirect.
Fixes#25506.
David Rosa
Alya Abbott