Added support for calculate and convert for data fields.

@examples calculate (its all up to you)

fields: [{
    name: 'id',
    type: 'Number'
}, {
    name: 'name',
    defaultValue: 'Defaults To Name',
    /**
     * @config data       the record
     * @config field       the field definition
     * @config rawData the data as they come initially
     */
    calculate: (data, field, rawData) => {
        // foo will not exist in data, but in this example 
        // foo is delivered with the initial data
        if (rawData) return rawData.foo;

        data.name ??= field.defaultValue;
        return 'I am ' + data.name;
    }
}]

convert (will run the standard afterwards, like minLength and maxLength)

fields: [{
    name: 'id',
    type: 'Number'
}, {
    name: 'name',
    defaultValue: 'Defaults To Name',
    convert: value => 'I am ' + value
}]