- #4339: remove non-recommended JSON formatter constructors
- affects `JsonInputFormatter`, `JsonOutputFormatter`, `JsonPatchInputFormatter`
- `JsonOutputFormatter` cleanup also impacts `JsonHelper`
- rename and make `SerializerSettingsProvider` class public; use it as appropriate
- #4409: make `SerializerSetings` properties get-only and `protected`
- affects `JsonInputFormatter`, `JsonOutputFormatter`
Recommended patterns:
- change `JsonSerializerSettings` values in `MvcJsonOptions` for almost all customizations
- find `JsonOutputFormatter` in `MvcOptions.OutputFormatters` when limiting per-result formatters
- start with `JsonSerializerSettingsProvider.CreateSerializerSettings()` when customizing a per-result formatter
