Use configured encoding during JiBX unmarshalling

Before this change JibxMarshaller did not use the configured encoding
when unmarshalling XML. This caused issues when content being
unmarshalled was not encoded using the default encoding.

This commit fixes the issue by passing configured encoding to JiBX so
it gets used when unmarshalling instead of the default encoding.

Issue: SPR-7865

spring-oxm/src/test/resources/org/springframework/oxm/jibx/binding.xml

@@ -8,6 +8,7 @@
     </mapping>
     <mapping name="flight" class="org.springframework.oxm.jibx.FlightType">
         <namespace uri="http://samples.springframework.org/flight" default="elements"/>
+        <value name="airline" field="airline" usage="optional"/>
         <value name="number" field="number" usage="required"/>
     </mapping>
 </binding>