RSRP-453533: Make all fields readonly in file/project/solution does not work

Given a class with more than one field that is a candidate to be made readonly, the UI offers the option to convert fields in the current file, project or solution - but none of these options have any effect and no error is reported.

The following class demonstrates this:

// ReSharper disable UnusedMember.Global
// ReSharper disable MemberCanBePrivate.Global

namespace ResharperReadonlyInFile
{
    public class MyClass
    {
        public string Field1 = "Blah";

        public string Field2 = "Blah2";

        public string Thing()
        {
            return $"{Field1}{Field2}";
        }
    }
}

None of these options work.

This occurs for both static and non-static fields.