Convert the raylet client (the code in local_scheduler_client.cc) to proper C++. (#3511)

* refactoring

* fix bugs

* create client class

* create client class for java; bug fix

* remove legacy code

* improve code by using std::string, std::unique_ptr rename private fields and removing legacy code

* rename class

* improve naming

* fix

* rename files

* fix names

* change name

* change return types

* make a mutex private field

* fix comments

* fix bugs

* lint

* bug fix

* bug fix

* move too short functions into the header file

* Loose crash conditions for some APIs.

* Apply suggestions from code review

Co-Authored-By: suquark <suquark@gmail.com>

* format

* update

* rename python APIs

* fix java

* more fixes

* change types of cpython interface

* more fixes

* improve error processing

* improve error processing for java wrapper

* lint

* fix java

* make fields const

* use pointers for [out] parameters

* fix java & error msg

* fix resource leak, etc.

python/setup.py

@@ -23,7 +23,7 @@ ray_files = [
     "ray/core/src/ray/thirdparty/redis/src/redis-server",
     "ray/core/src/ray/gcs/redis_module/libray_redis_module.so",
     "ray/core/src/plasma/plasma_store_server",
-    "ray/core/src/ray/raylet/liblocal_scheduler_library_python.so",
+    "ray/core/src/ray/raylet/libraylet_library_python.so",
     "ray/core/src/ray/raylet/raylet_monitor", "ray/core/src/ray/raylet/raylet",
     "ray/WebUI.ipynb"
 ]