Fix for NPE when creating ProtobufHttpMessageConverter without ExtensionRegistryInitializer
Use X-Forwarded-Prefix in ServletUriComponentsBuilder

Issue: SPR-12500
Merge pull request #702 from aantono/master

Fix for NPE when creating ProtobufHttpMessageConverter without ExtensionRegistryInitializer
Consistent resolution of Class methods and static methods

Issue: SPR-12502
Update supported WebSocket runtimes in the reference documentation