Provide a twig test to test if a value is readable before applying the readable_enum filter

[Ezar101]

I did this in a project based on the findOccurences() function of the ReadableEnumValueTwigExtension class, but I don't know if I would have time to make a contribution.

https://gist.github.com/Ezar101/02bb272eeeeee3a3818e8272606f3011

Thank You