`[DataType]` and `[DisplayFormat]` ignored when choosing `@Html.Display()` and `@Html.Editor()` templates

[dougbu]

This is a functional gap compared with MVC 5.2. For example it leads to incorrect templates for @Html.Display() and @Html.Editor().

The current implementation of CachedModelMetadata<TPrototypeCache> does not override the DataTypeName property as it should. Value should be based on [DataType] or (for the special case of the "html" choice) [DisplayFormat] attributes in the model.

[dougbu]

Need to set ModelMetadata.DataTypeName based on attributes, as described above.

Between this bug and #963, only a few of the default templates get chosen automatically -- based just on the model's Type and whether it's a complex object or collection. Manual ModelMetadata changes are required to have the "Date", "DateTime-local", "EmailAddress", "HiddenInput", "Html", "Password", "PhoneNumber", "Time", or "Url" templates picked up.