support for System.Exception.get_InnerException

[joprice]

Would it be possible to support System.Exception.get_InnerException?

It currently fails at compile time with error FABLE: System.Exception.get_InnerException is not supported by Fable.

For javascript, it could map to the cause parameter:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error/cause#rethrowing_an_error_with_a_cause

and on python

https://python-future.org/compatible_idioms.html#raising-exceptions raise_from

Not sure about other targets, but it can be helpful for debugging to make use of the underlying platform's ability to decorate an error with additional context information, but not lose track of the original message and trace.