C# JsonFormatter does not have a preservingProtoFieldNames method

[fractus]

What language does this apply to?
If it's a proto syntax change, is it for proto2 or proto3?
If it's about generated code change, what programming language?
C#, Proto3

Describe the problem you are trying to solve.
The JsonFormatter does not have a preservingProtoFieldNames method like Java; see JsonFormat.Printer

Describe the solution you'd like
Adding the method, like in Java; simliar issue #2029

Describe alternatives you've considered
None

Additional context
Add any other context or screenshots about the feature request here.
Example:

message FullName {
  string first_name = 1;
  string last_name = 2;
}

var name = new FullName {FirstName = "John", LastName = "Doe"};
var jsonName = JsonFormatter.Default.Format(name);
Console.Out.WriteLine(jsonName);

Output is:

{ "firstName": "John", "lastName": "Doe" }