- #3227
- much of change is to tests, creating and passing `ModelMetadata`
- updated `InputFormatterContext` to make `ModelMetadata` available to `JsonInputFormatter`
- walk `ModelMetadata` tree to get information about property with an issue
- add missing `null` checks in `ModelStateDictionaryExtensions`
- Making TagBuilder's InnerHtml an IHtmlContent.
- Delay encoding until the content is written.
- Moving BufferedHtmlContent to Common cos it is used in aspnet/Razor also.
- Changing GenerateOption to take in a string and create StringHtmlContent.
- This reduces the space used by around 13%.