* Add a 'Set' method to AutomationRemoteExtensionTarget. All AutomationRemoteObject subclasses require this but seemed to have been left out of the original implementation.
* Add 'IsExtensionTarget' and 'AsExtensionTarget' methods to AutomationRemoteAnyObject to enable check / casting to AutomationRemoteExtensionTarget.
* Add a deprecation comment to AutomationRemoteExtensionTarget::IsExtensionTarget. I think this was a misunderstanding of where this needed to be.

* Add a UiaTypeBaseWithExtensionSupport template class which subclasses UiaTypeBase and adds IsExtensionSupported and CallExtension methods, moved from UiaElement.
* UiaElement and UiaTextRange now inherit from UiaTypeBaseWithExtensionSupport rather than UiaTypeBase. This makes IsExtensionSupported and CallExtension methods again available on UiaElement, but also now UiaTextRange.
* Add a new UiaConnectionBoundObject class, which inherits from UiaTypeBaseWithExtensionSupport. It contains no other real features of its own a part from being constructable from / convertable to AutomationRemoteExtensionTarget remotely and IUnknown locally. This can be used as a generic connection-bound object, such as sometimes returned from CallExtension, which represents a custom extension pattern. Previously the caller had to treat the object as a UiaElement, even though it was not really.