UserStatusScreen: Trim entered text status before interpreting it

This seems helpful. It's easy to end up with leading or trailing
spaces in a text input, and want them to be treated as though they
weren't there. The server may even trim the text status too, I'm not
sure.

Note that we don't do this by fussing with the actual value of the
text input. That'd be easy to do, since we're using Input as a
controlled input -- but it would be a misuse of that control. In
particular, we'd introduce a bug like the following, on a topic
input, fixed in zulip#5098:

> Some bug prevented adding a space at the end of what I was typing
> specifically on the topic and maybe stream input (the space would
> appear and then immediately disappear, I think) ... so I was only
> able to create the topic "bog plants" by typing "bogplants" and
> then moving my cursor.

src/user-statuses/UserStatusScreen.js

@@ -37,7 +37,8 @@ type Props = $ReadOnly<{|
   route: RouteProp<'user-status', void>,
 |}>;
 
-const statusTextFromInputValue = (v: string): $PropertyType<UserStatus, 'status_text'> => v || null;
+const statusTextFromInputValue = (v: string): $PropertyType<UserStatus, 'status_text'> =>
+  v.trim() || null;
 
 const inputValueFromStatusText = (t: $PropertyType<UserStatus, 'status_text'>): string => t ?? '';