Adds a new tab with the resolve/unresolve topic instructions for
mobile app users.
Makes the instructions a little more explicit so that users know they
won't see the menu unless they press and hold the topic long enough.
Also improves the wording of the instructions to access the
long-press menu so that users are more likely to read it as saying
that the whole area of a given topic, extending the whole width of
the screen, is the region they can press to act on that topic.
Fixes#22144.
Adds a "Mobile" tab with straightforward instructions for accessing
the long-press menu using two new macros.
Knowing where to access the long-press menu is intuitive, except when
the user is in a topic narrow. It's not immediately obvious that the
top bar can be long-pressed so this adds a "Tip block" using a new macro
to clarify things in this scenario.
Also, this combines the instructions for Desktop and Web into a single
tab because the numbered steps work on both platforms. So this documents
the alternate method via the browser's address bar as a "Tip block" to
avoid stacking alternative numbered steps into a single tab.
This updates the stream and message link instructions too.
Fixes: #22147.
David Rosa