Fix generic signature of AdvancedCacheLoader.process(...)

... so that implementations don't need to resort to type erasure to invoke CacheLoaderTask.processEntry(...).

Otherwise cache loader implementations need to resort to tactics like:
https://github.com/pferraro/wildfly/blob/infinispan/clustering/infinispan/src/main/java/org/jboss/as/clustering/infinispan/persistence/file/FileStore.java#L185