Expose the inner rust side error type via the exception on the c++ side

[weiznich]

This is an attempt to address https://github.com/dtolnay/cxx/issues/870 and similar issues.

I attempt to expose more information on the underlying rust error by including the the original error into the c++ side exception. This allows accessing any error related information from the c++ side as well, assuming that the error type is exposed as part of the cxx bridge definition.

I deliberately open this PR in this state, to gather some feedback on the design idea before spending to much time on details.

[weiznich]

Gentle ping to @dtolnay to get some input on the general design and whether this feature is wanted or not.

[dtolnay]

I am interested for this crate to support this, but I will not be able to prioritize iterating on the implementation in the near term.