Consider making `ArgumentConverter#convert(Object, FieldContext)` non-default

convert(Object, FieldContext) was introduced as a default method for backward compatibility in #4342.

I've recently implemented a few new argument converters and consistently managed to overlook overriding that method

Would you consider a breaking change by making it non-default in version 6?

Deliverables

• convert(@Nullable Object source, FieldContext context) is no longer a default method