Do not force json to use JSON functions

[Tobbeman]

We are using scaffolding to create our database classes. Sadly, the scaffold does not support json on the json field, instead opting for string.

This change will let the user use JSON functions more freely

[lara-ec]

In case this is helpful for anyone: our solution for this was editing the EntityType.t4 template to not annotate the string columns as json:

before:

            foreach (var dataAnnotation in dataAnnotations)
            {
#>
    <#= code.Fragment(dataAnnotation) #>
<#
            }

after:

            foreach (var dataAnnotation in dataAnnotations)
            {
                var annotation = dataAnnotation;
                if (
                    dataAnnotation.Type == typeof(System.ComponentModel.DataAnnotations.Schema.ColumnAttribute)
                    && dataAnnotation.NamedArguments.TryGetValue("TypeName", out var typeName)
                    && typeName is "json"
                )
                {
                    annotation = new AttributeCodeFragment(
                        annotation.Type,
                        annotation.Arguments,
                        annotation.NamedArguments.Where(n => n.Key != "TypeName").ToDictionary()
                    );

#>
    // this is a json column
<#
                }
#>
    <#= code.Fragment(annotation) #>
<#
            }