Feature Add Validation to ReactiveProperty

[ChrisPulman]

What kind of change does this PR introduce?

Feature for #3771

What is the current behavior?

ReactiveProperty has basic functionality

What is the new behavior?

ReactiveProperty now supports Validation through INotifyDataErrorInfo
AddValidation and AddValidationError methods added to attach the ReactiveProperty to the Validation mechanism
CheckValidation and Refresh exist to re-evaluate the Validation

MyReactiveProperty = new ReactiveProperty<string>()
    .AddValidation(() => MyReactiveProperty)
    .AddValidationError(s => string.IsNullOrWhiteSpace(s) ? "required" : null);

What might this PR break?

None expected.

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Other information:

[github-actions]

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