A couple of potentialModelMetadata additions came up in offline conversations about#5676:

• haveModelMetadata implementIModelMetadataProvider. This should significantly reduce the shenanigans we have around ensuring bothModelMetadata and its provider are available. E.g.
  • many contexts contain bothModelMetadata andIModelMetadataProvider properties.
  • ModelBinderFactory gets the provider from DI thoughModelBinderFactoryContext contains aModelMetadata property.
  • ExpressionMetadataProvider methods contain bothViewDataDictionary (which hasModelMetadata) andIModelMetadataProvider parameters.
• add aContainerMetadata property. This seem slightly redundant ifModelMetadata implementsIModelMetadataProvider but would be convenient.
  • Note information about the containingproperty is not static and cannot be maintained inModelMetadata.