Previously, if a user declared a custom conversionService bean that
was not an ApplicationConversionService instance, the binder lost
the ability to convert a String to a Duration (along with any other
conversions that are specific to ApplicationConversionService).

This commit updates BindConverter so that, if the ConversionService
with which it is created is not an ApplicationConversionService, it
will use one as an additional service when performing conversion.

Closes gh-12237