InputFormatter errors reported by JsonContractResolver should use the entire model prefix as the model state key.

[harshgMSFT]

Consider the following two examples :

Example 1

   public class Person
   {
        [FromBody]
        [Required]
        public Address Address { get; set; }
   }

   public class Address
   {
         public int Zip { get; set; }
   }

Request body ""
In this case the error key would be "" and not "prefix.Address" (assuming there is a prefix because of additional metadata/positioning for/of the Person model).
Also the model state dictionary incorrectly has two keys
Key 1 : ""
Key 2 : Address -> This gets added because the validator looks for a key Address and not "" to determine if validation has been done for property Address.
In this case there should have been only two keys Address and it should be invalid.

Example 2

   public class Person
   {
        [FromBody]
        public Address Address { get; set; }
   }

   public class Address
   {
        public string Street { get; set; }

        [Required]
         public int Zip { get; set; }
   }

Request body { "Street" : "Some street" }
In this case the error key would be "Street" and not "prefix.Address.Street" (assuming there is a prefix because of additional metadata/positioning for/of the Person model).
Also the model state dictionary incorrectly has three keys
Key 1 : ""
Key 2 : Street
Key 3: Zip -> This gets added as a valid entry because the validator looks for a key Zip and not "" to determine if validation has been done for property Zip.
In this case there should have been only two keys Address.Street and Address.Zip and the second one should be invalid.

The fix for this we would have to make the model state keys consistent with the rest of the model binding system. In all cases it should add the full prefixed version as the error key.

The fix to this might require #2330 to be fixed.