Added a numberOfActions get property on the BrainParameters (#3571)

* Added a numberOfActions get property on the BrainParameters

* forgot one place to replace

* [skip ci] numberOfActions --> numActions

com.unity.ml-agents/Runtime/Agent.cs

             // should stay the previous action before the Done(), so that it is properly recorded.
             if (m_Action.vectorActions == null)
             {
-                if (param.vectorActionSpaceType == SpaceType.Continuous)
-                {
-                    m_Action.vectorActions = new float[param.vectorActionSize[0]];
-                    m_Info.storedVectorActions = new float[param.vectorActionSize[0]];
-                }
-                else
-                {
-                    m_Action.vectorActions = new float[param.vectorActionSize.Length];
-                    m_Info.storedVectorActions = new float[param.vectorActionSize.Length];
-                }
+                m_Action.vectorActions = new float[param.numActions];
+                m_Info.storedVectorActions = new float[param.numActions];
             }
         }
 
         {
             Debug.LogWarning("Heuristic method called but not implemented. Returning placeholder actions.");
             var param = m_PolicyFactory.brainParameters;
-            var actionSize = param.vectorActionSpaceType == SpaceType.Continuous ?
-                param.vectorActionSize[0] :
-                param.vectorActionSize.Length;
-            return new float[actionSize];
+            return new float[param.numActions];
         }
 
         /// <summary>

com.unity.ml-agents/Runtime/Policies/BrainParameters.cs

         /// </summary>
         public SpaceType vectorActionSpaceType = SpaceType.Discrete;
 
+        public int numActions
+        {
+            get{
+                switch(vectorActionSpaceType){
+                    case SpaceType.Discrete:
+                        return vectorActionSize.Length;
+                    case SpaceType.Continuous:
+                        return vectorActionSize[0];
+                    default:
+                        return 0;
+                }
+            }
+        }
+
         /// <summary>
         /// Deep clones the BrainParameter object.
         /// </summary>