Added Action masking for Space.sample() (#2906)

* Allows a new RNG to be generated with seed=-1 and updated env_checker to fix bug if environment doesn't use np_random in reset

* Revert "fixed `gym.vector.make` where the checker was being applied in the opposite case than was intended to (#2871)"

This reverts commit 519dfd9117.

* Remove bad pushed commits

* Fixed spelling in core.py

* Pins pytest to the last py 3.6 version

* Add support for action masking in Space.sample(mask=...)

* Fix action mask

* Fix action_mask

* Fix action_mask

* Added docstrings, fixed bugs and added taxi examples

* Fixed bugs

* Add tests for sample

* Add docstrings and test space sample mask Discrete and MultiBinary

* Add MultiDiscrete sampling and tests

* Remove sample mask from graph

* Update gym/spaces/multi_discrete.py

Co-authored-by: Markus Krimmel <montcyril@gmail.com>

* Updates based on Marcus28 and jjshoots for Graph.py

* Updates based on Marcus28 and jjshoots for Graph.py

* jjshoot review

* jjshoot review

* Update assert check

* Update type hints

Co-authored-by: Markus Krimmel <montcyril@gmail.com>

gym/spaces/box.py

@@ -3,6 +3,7 @@ from typing import Dict, List, Optional, Sequence, SupportsFloat, Tuple, Type, U
 
 import numpy as np
 
+import gym.error
 from gym import logger
 from gym.spaces.space import Space
 from gym.utils import seeding
@@ -146,7 +147,7 @@ class Box(Space[np.ndarray]):
         else:
             raise ValueError("manner is not in {'below', 'above', 'both'}")
 
-    def sample(self) -> np.ndarray:
+    def sample(self, mask: None = None) -> np.ndarray:
         r"""Generates a single random sample inside the Box.
 
         In creating a sample of the box, each coordinate is sampled (independently) from a distribution
@@ -157,9 +158,17 @@ class Box(Space[np.ndarray]):
         * :math:`(-\infty, b]` : shifted negative exponential distribution
         * :math:`(-\infty, \infty)` : normal distribution
 
+        Args:
+            mask: A mask for sampling values from the Box space, currently unsupported.
+
         Returns:
             A sampled value from the Box
         """
+        if mask is not None:
+            raise gym.error.Error(
+                f"Box.sample cannot be provided a mask, actual value: {mask}"
+            )
+
         high = self.high if self.dtype.kind == "f" else self.high.astype("int64") + 1
         sample = np.empty(self.shape)