Add chat.max_announcement_length cvar (#23571)

Add chat.max_announcement_length cvar (#23571)

* Add announce message length to UI and make a cvar for it

* Update comm console server-side trim to use the cvar

* Rely on the new OnTextChanged event

Because OnKeyBindUp only works for keys that have binds

* Add a similar indicator to nukies' war declaration UI

* Remove message length indicators for now cuz it requires the engine update

* Rename cvar slightly

* Refactor duplicated code to a helper method

* Remove message trimming from *Window class as it's better to live in the BoundUserInterface where the other message handling happens

* Rename to chat.max_announcement_length