Change default json serialization behavior in 2.0 to match 1.0

In 1.0, a property `FooBar` is serialized to `FooBar` in json. In the .NET Core port, it is serialized to `fooBar`. We should change the default to match 1.0.

@fabiocav says this is probably because ASP.NET has different default serialization settings.

No file or test is identified. Start by tracing the .NET Core port's default JSON serialization settings and comparing them with the ASP.NET defaults mentioned in the issue. Confirm the expected FooBar casing against 1.0 and add coverage for the default behavior; done means the port serializes properties with the legacy casing by default.

Written by the indexing model from the issue text.