Make Parameter & PropertyDeclaration Classes Instead of Records

[jorgerangel-msft]

This PR updates the Parameter and PropertyDeclaration types by converted them into classes and adds constructors to build both types from an InputModelProperty.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[ArcturusZhang]

So I do not think we want to close the Parameter, FieldDeclaration and PropertyDeclaration classes for users and only leave a few entry points for them, as far as I could read from our comments, these entry points are:

• from input parameter/property
• from a known list of parameters (how about field and property?)

These classes are defining a member in CSharp language therefore I think when our plugin writer is writing something, they might always need to write something that does not come from the spec, therefore they might need to construct their own parameter or field or property.
For instance in the patch implementation, our current design introduces quite a few extra fields and properties, for example the backing field of the property, the IsChanged property for the model itself, some of them do not come from a input type.
Therefore I think we should keep those ctors to construct a parameter/field/property from scratch public.

Also I think it makes more sense to construct a parameter/field/property from input if those are not ctors but static methods.