Remove DistinctUntilChanged from WhenAnyValue

[user98392]

When WhenAnyValue is used for example on a boolean property it doesn't react to all the changes and that is a problem.
The reason is DistinctUntilChanged that is sitting on the last line of the SubscribeToExpressionChain method in the ReactiveNotifyPropertyChangedMixin class.

[glennawatson]

This won't be changing. It will be a breaking change for all users.

Possibly new operators could be added since this won't be a breaker binary change for existing users, and a change of existing functionality.