An annotation used to mark methods to indicate code capable of being a
fallback converter which are then auto-discovered using
The difference between a regular @Converter and a @FallbackConverter
is that the fallback is resolved at last if no regular converter could be found.
Also the method signature is scoped to be generic to allow handling a broader range
of types trying to be converted. The fallback converter can just return null
if it can not handle the types to convert from/to.