Send schema errors to OnError callback in all cases

[swannman]

A schema lookup occurs when a predicate filter is applied to a record. If the schema lookup fails, a krabs::could_not_find_schema exception is thrown. This exception was previously unhandled and caused an exception to propagate on the main trace thread.

A better way to handle this is to catch the schema exception and notify the application via an OnError delegate. An OnError delegate existed on the C++/CLI Provider object but not on the native event_filter and provider objects nor on the C++/CLI EventFilter.

This change finishes the implementation of error handling on the managed and native layers:

• it adds an OnError delegate to the C++/CLI EventFilter class, wires it up to a new callback in event_filter, and adds an appropriate try/catch in event_filter::on_event to use the new callback
• it wires up the existing OnError delegate on the C++/CLI Provider to a new callback in provider and adds an appropriate try/catch in base_provider::on_event to use the new callback
• it adds an interface for EventRecordError to allow OnError handlers to be unit-tested

[swannman]

Thanks @henriblMSFT for the review! Updated with your feedback.