Improve Editing Channel errors

[karolis-zukauskas]

Is your feature request related to a problem? Please describe.
Attempting to delete an Element from a Channel that is not allowed results in an Error that has no "type" - errorNumber is not set - error in question is thrown here.

Calling code cannot catch such error (without comparing against message field).

Bonus: if this error is passed to the Frontend (in case of an electron desktop app), the error object is of class BackendError (IModelError) and has an errorNumber of 0 - which is IModelStatus.Success.

Describe the solution you'd like
I'd like to be able to catch such error by checking its "type" and react to it e.g. by showing user a message that he cannot make changes to the Element(s).

Is there something I need to be calling before attempting to edit elements?

Additional context
iTwin.js: 4.10.2