Seeding update (#2422)

* Ditch most of the seeding.py and replace np_random with the numpy default_rng. Let's see if tests pass

* Updated a bunch of RNG calls from the RandomState API to Generator API

* black; didn't expect that, did ya?

* Undo a typo

* blaaack

* More typo fixes

* Fixed setting/getting state in multidiscrete spaces

* Fix typo, fix a test to work with the new sampling

* Correctly (?) pass the randomly generated seed if np_random is called with None as seed

* Convert the Discrete sample to a python int (as opposed to np.int64)

* Remove some redundant imports

* First version of the compatibility layer for old-style RNG. Mainly to trigger tests.

* Removed redundant f-strings

* Style fixes, removing unused imports

* Try to make tests pass by removing atari from the dockerfile

* Try to make tests pass by removing atari from the setup

* Try to make tests pass by removing atari from the setup

* Try to make tests pass by removing atari from the setup

* First attempt at deprecating `env.seed` and supporting `env.reset(seed=seed)` instead. Tests should hopefully pass but throw up a million warnings.

* black; didn't expect that, didya?

* Rename the reset parameter in VecEnvs back to `seed`

* Updated tests to use the new seeding method

* Removed a bunch of old `seed` calls.

Fixed a bug in AsyncVectorEnv

* Stop Discrete envs from doing part of the setup (and using the randomness) in init (as opposed to reset)

* Add explicit seed to wrappers reset

* Remove an accidental return

* Re-add some legacy functions with a warning.

* Use deprecation instead of regular warnings for the newly deprecated methods/functions

docs/creating_environments.md

@@ -50,6 +50,7 @@
 
 * `gym-foo/gym_foo/envs/foo_env.py` should look something like:
   ```python
+  from typing import Optional
   import gym
   from gym import error, spaces, utils
   from gym.utils import seeding
@@ -61,7 +62,8 @@
       ...
     def step(self, action):
       ...
-    def reset(self):
+    def reset(self, seed: Optional[int] = None):
+      super().reset(seed=seed)
       ...
     def render(self, mode='human'):
       ...