Consider updating AccessibleObject to allow enabling UIA and IAccessibleEx from custom controls

At this moment there is no way to add/implement modern accessibility patterns for custom controls that inherit from Control other than implementing these from scratch.

Adding IAccessibleEx implementation requires to disable already existing internal IAccessibleEx implementation.

Implementing UIA also requires to override WndProc method which may be not trivial for C# developers.

So there are few ways to work around this: to open corresponding APIs to enable/disable UIA/IAccessibleEx-provided accessibility or enable modern accessibility implementation for all controls by default.