[Enhancement] Downgrade InvokeAction method of class EventSubscription access from public to protected

[BruceLeeCorner]

Summary

I figure , it is better to downgrade access of InvokeAction method in class EventSubscription from public to protected.

API Changes

Just change 3 files EventSubscription.cs DispatcherEventSubscription.cs BackgroundEventSubscription.cs.

e.g.

change

public virtual void InvokeAction(Action action)
{
    if (action == null) throw new ArgumentNullException(nameof(action));

    action();
}

to

protected virtual void InvokeAction(Action action)
{
    if (action == null) throw new ArgumentNullException(nameof(action));

    action();
}