Previously AbstractMessageConverter did not have a ContentTypeResolver
configured by default. However the Java config and XML namespace in
spring-messaging and spring-websocket always configured one.
This change ensures every AbstractMessageConverter is configured with an
instance of DefaultContentTypeResolver by default. This makes sense since
all the resolver does is make an attempt to find a content type to use
for matching. If it can't it returns null and it's up to the converter
to decide whether it can convert or not.
Issue: SPR-11462
0da1eefd74