[Java] Add killActor API in Java (#6728)

* Add killActor API in Java

* fix javadoc

* update test case

* Address comments

java/api/src/main/java/org/ray/api/Ray.java

@@ -130,6 +130,7 @@ public final class Ray extends RayCall {
 
   /**
    * Set the async context for the current thread.
+   *
    * @param asyncContext The async context to set.
    */
   public static void setAsyncContext(Object asyncContext) {
@@ -180,6 +181,16 @@ public final class Ray extends RayCall {
     runtime.setResource(resourceName, capacity, UniqueId.NIL);
   }
 
+  /**
+   * Kill the actor immediately. This will cause any outstanding tasks submitted to the actor to
+   * fail and the actor to exit in the same way as if it crashed.
+   *
+   * @param actor The actor to be killed.
+   */
+  public static void killActor(RayActor<?> actor) {
+    runtime.killActor(actor);
+  }
+
   /**
    * Get the runtime context.
    */

java/api/src/main/java/org/ray/api/runtime/RayRuntime.java

@@ -76,6 +76,13 @@ public interface RayRuntime {
    */
   void setResource(String resourceName, double capacity, UniqueId nodeId);
 
+  /**
+   * Kill the actor immediately.
+   *
+   * @param actor The actor to be killed.
+   */
+  void killActor(RayActor<?> actor);
+
   /**
    * Invoke a remote function.
    *