Fix S6966 FP: Don't raise on XmlReader and XmlWriter methods

[denis-troller]

Description

Rule S6966 raises on XMLReader methods, however the ability to use these methods successfully depends on whether the object was created with the Async flag set to true in its settings.
Unless the creation is in scope, we should not raise on those as the ability to use those methods might not be under the user's control.

[mary-georgiou]

What the description mentions happens also for XmlWriter methods.

As it's complicated for now to support the scenario where we check if the settings provided to the XmlReader/Writer constructor have the async property set as true (requires SE), we'll exempt all the methods coming from XmlReader and XmlWriter.