Deserializer should support only getter for IDictionary properties

[steveharter]

For objects that expose an IDictionary<,> currently the deserializer requires a public property setter but ideally it should not - it should only require a public getter. The POCO type would create the dictionary itself (likely from within its constructor) and return it from the public getter.

Note that IList<> currently supports this mode of not having a setter.

Implementation support for this is incremental:

• Add a IsPropertyDictionary to ReadStackFrame
• Add PopStackOnEndObject to ReadStackFrame and use accordingly in JsonSerializer.HandleStartObject\HandleEndObject
• Modify ApplyValueToEnumerable to handle the property case.
• Add tests for this including when there is a public setter but the dictionary is already initialized (we should just use the existing instance)
• ...