Previously, to use a custom ConfigurableWebBindingInitializer, it was
necessary to extend WebMvcConfigurationSupport and override
getConfigurableWebBindingInitializer. This had the unwanted
side-effect of switching off the auto-configuration of Spring MVC.

This commit updates the auto-configuration to look for a
ConfigurableWebBindingInitializer bean and register it with Spring
MVC.

Closes gh-2526