Refactor ID Serial 1: Separate ObjectID and TaskID from UniqueID (#4776)

* Enable BaseId.

* Change TaskID and make python test pass

* Remove unnecessary functions and fix test failure and change TaskID to
16 bytes.

* Java code change draft

* Refine

* Lint

* Update java/api/src/main/java/org/ray/api/id/TaskId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update java/api/src/main/java/org/ray/api/id/BaseId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update java/api/src/main/java/org/ray/api/id/BaseId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Update java/api/src/main/java/org/ray/api/id/ObjectId.java

Co-Authored-By: Hao Chen <chenh1024@gmail.com>

* Address comment

* Lint

* Fix SINGLE_PROCESS

* Fix comments

* Refine code

* Refine test

* Resolve conflict

python/ray/actor.py

@@ -17,7 +17,6 @@ from ray.function_manager import FunctionDescriptor
 import ray.ray_constants as ray_constants
 import ray.signature as signature
 import ray.worker
-from ray.utils import _random_string
 from ray import (ObjectID, ActorID, ActorHandleID, ActorClassID, TaskID,
                  DriverID)
 
@@ -308,7 +307,7 @@ class ActorClass(object):
             raise Exception("Actors cannot be created before ray.init() "
                             "has been called.")
 
-        actor_id = ActorID(_random_string())
+        actor_id = ActorID.from_random()
         # The actor cursor is a dummy object representing the most recent
         # actor method invocation. For each subsequent method invocation,
         # the current cursor should be added as a dependency, and then
@@ -670,7 +669,7 @@ class ActorHandle(object):
             # to release, since it could be unpickled and submit another
             # dependent task at any time. Therefore, we notify the backend of a
             # random handle ID that will never actually be used.
-            new_actor_handle_id = ActorHandleID(_random_string())
+            new_actor_handle_id = ActorHandleID.from_random()
         # Notify the backend to expect this new actor handle. The backend will
         # not release the cursor for any new handles until the first task for
         # each of the new handles is submitted.
@@ -780,7 +779,7 @@ def make_actor(cls, num_cpus, num_gpus, resources, max_reconstructions):
     Class.__module__ = cls.__module__
     Class.__name__ = cls.__name__
 
-    class_id = ActorClassID(_random_string())
+    class_id = ActorClassID.from_random()
 
     return ActorClass(Class, class_id, max_reconstructions, num_cpus, num_gpus,
                       resources)