These are no longer needed now that InteractiveCommand is a proper workspace language again. The completion service now exclusive operates on documents.

It's not unexpected at this location.

```LocalizableErrorArgument```, in particular, will not be ReferenceEquals
across 	```DiagnosticInfo``` instantiations.

 1. Wrap every async method in an exception filter that reports a
 non-fatal Watson, prints and error message, and then propagates the
 exception.  We do this so that dumps are taken before exceptions are
 stashed in tasks and the stack is unwound.

 2. Wrap the command filter in an exception filter that reports a
 non-fatal Watson, suppresses the error, and forwards to the next filter
 in the chain.  Propagated exceptions would just turn into useless
 dialogs.

 Fixes #4553

Exceptions in (or under) ```FinishExecute``` were being lost.  As a
result, some of our tests were passing incorrectly.

Instead of trying to manage everything ourselves using ```ContinueWith```
use ```async``` and let the system propagate exceptions for us.

This is intended to prevent this provider from being loaded in *normal*
C# files.

Fixes #4769

Since they can be used in subsequent submissions, they are always
considered to be used.

Fixes #4392

Pointer width was hardcoded - switched to using ```PointerToString```.

Bonus: Fix cast exception in attempt to report the failure.
Bonus: Make Native View hex lowercase to match the rest of the
ResultProvider.