Support Unicode Attribute

[RaymondHuy]

#19794 Support Unicode attribute

[smitpatel]

Figured out randomization. Tests don't round trip, they just build the model locally and try to generate code for it. Hence the model generation cannot actually have value conversion specified since relational scaffolding model factory does not generate such model. Further in scaffolding the unicode is inferred based on candidate clr type of string for SqlServer hence it is not explicitly scaffolded on the property either. So ideally what we get in the model is null for IsUnicode. Added additional code to print when IsUnicode is set to true. (Unlikely that we will ever need it but who knows if there is some database which has unicode false as default inference.
When field is mapped as property, we discover attributes on them, and UnicodeAttribute also works fine on them.

[smitpatel]

@RaymondHuy - Thank you for contribution.