Add option to get a single processed form value
RenderAllFormValuesViewHelper is the only option to get processed form values. There is no way to selectively retrieve the processed value of a single form element which would be useful e.g. for custom email templates which don't need all form values or need a custom order and placement of form values.
One option would be a
RenderFormValueViewHelper. The API method
FormDefinition::getElementByIdentifier() could be used internally to retrieve a requested form element. The value processing would be moved to a central location for both of these viewhelpers.