Ability to run some user code whenever a binding throws an exception

Realize we may do much more than what's scoped in title (trigger for any unhandled exception) but the scenario we have committed to resolve by end of this calendar year is:

> A customer wants to use an output binding (and not using with `Flush`). If the output binding hits an exception, I need some way to get the context of the execution and the context of the exception to handle it.

We know richer bindings could allow something like `FlushAsync` for non-.NET languages (and for mitigation for now .NET users can use an `ICollectorAsync` with `FlushAsync` to catch exceptions there), but need something shorter term.

Have vetted with a few customers and the idea of having an "Exception trigger" for an "Exception function" works fine. As long as the trigger has the right context of the execution that hit an exception, and exception details, so it can be handled correctly.

Start by reading the proposed customer scenario and the discussion about output bindings, FlushAsync, and an exception trigger. Determine how execution context and exception details should reach the proposed exception function, and treat a defined trigger contract and handling path as done; the issue names no files or tests to run.

Written by the indexing model from the issue text.