cleanup series of webxdc info messages (#3395)

* clarify webxdc reference wrt info-messages

* add from_id parameter to add_info_msg_with_cmd()

* flag webxdc-info-messages as such

* set from_id to sender for webxdc-info-messages

* test additional webxdc info properties

* do not add series of similar info messages

instead, if on adding the last info message
is already from the same webxdc and sender,
just update the text

* test cleanup of webxdc info messages series

* update changelog

* make clippy happy

there is no real complexity in the args,
so allowing one more arg is probably fine.

if really wanted, we can refactor the function in another pr;
this pr is already complex enough :)

* use cleaner function names and comments

* clarify CHANGELOG

draft/webxdc-dev-reference.md

@@ -34,8 +34,9 @@ To get a shared state, the peers use `sendUpdate()` to send updates to each othe
 - `update`: an object with the following properties:  
     - `update.payload`: any javascript primitive, array or object.
     - `update.info`: optional, short, informational message that will be added to the chat,
-       eg. "Alice voted" or "Bob scored 123 in MyGame";
-       usually only one line of text is shown,
+       eg. "Alice voted" or "Bob scored 123 in MyGame".
+       usually only one line of text is shown
+       and if there are series of info messages, older ones may be dropped.
        use this option sparingly to not spam the chat.
     - `update.document`: optional, name of the document in edit,
        must not be used eg. in games where the Webxdc does not create documents