Add support for setter protection level for ObservableProperty

[sensslen]

Overview

When using the [ObservableProperty] attribute to generate the code for the observable property, the protection level of the generated setter is always public

API breakdown

public enum SetterProtection
{
    Public,
    Protected,
    Private
}


[ObservableProperty(SetterProtection = SetterProtection.Private)]
private int _someValue;

Usage example

[ObservableProperty(SetterProtection = SetterProtection.Private)]
private int _someValue;

Breaking change?

No

Alternatives

I am not aware of any

Additional context

I do quite often want to provide readonly properties for binding in xaml. These properties should not be set from xaml. While I can make sure this is how things are done, I don't get any support from the Toolkit (and if the xaml is wrong and sets such a property, It will silently work instead of causing a binding error).

Help us help you

Yes, but only if others can assist

[Sergio0694]

Duplicate of #291.
Superseded by #555.