doc: add error documentation
This adds error documentation, covering "JS errors" and "system errors." It is roughly a continuation of this PR, with some remaining comments cleaned up.
R=@trevnorris
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This adds error documentation, covering "JS errors" and "system errors." It is roughly a continuation of this PR, with some remaining comments cleaned up.
R=@trevnorris