Handle case-insensitive JSON claim value types.

[josephdecock]

This updates our serialization behavior so that we treat claims with either our json value type constant or the System.IdentityModel json value type constant the same. Prior to this change, we would serialize json with the System.IdentityModel as an escaped string instead of json, while our json value type constant would become json in the claims.

After this change, either constant will work to put JSON into your claims. For example, code like this in a profile service will now serialize the claims as JSON, instead of a string containing escaped quotes:

var payload = 
"""
{
  "nested": {
    "sample": "value"
  }
}
""";
context.IssuedClaims.Add(new Claim("json", payload, System.IdentityModel.Tokens.Jwt.JsonClaimValueTypes.Json))