Enable RedundantModifier checkstyle, add fixer

Add `fixModifiers.gradle` to run after `check` task.

The `RedundantModifierChecker` doesn't catch all errors at once.
We need run `check -> fixModifiers` pair several times to reach `SUCCESSFUL`.

The `fixThis` has been ported from the SA, but without applying.

* Polishing for `fixModifiers.gradle`
* Fix all redundant modifier with the `fixModifiers.gradle`

NOTE: Since all these task modify files on Windows we have to run them with the `-Dfile.encoding=UTF-8`.
Otherwise they are read and write with the Windows default `cp1251` making them incompatible with Unix system.

spring-integration-redis/src/main/java/org/springframework/integration/redis/outbound/RedisStoreWritingMessageHandler.java

@@ -480,6 +480,6 @@ public class RedisStoreWritingMessageHandler extends AbstractMessageHandler {
 	}
 
 	private interface PipelineCallback {
-		public void process();
+		void process();
 	}
 }