Fixed entities not being deselected when entering game mode in editor.

added protections around physx AZ::Events handlers that are connected/disconnected on selection events.
jira: LYN-2998

Code/Framework/AzToolsFramework/AzToolsFramework/Entity/EditorEntityContextComponent.cpp

@@ -491,6 +491,14 @@ namespace AzToolsFramework
 
         EditorEntityContextNotificationBus::Broadcast(&EditorEntityContextNotification::OnStartPlayInEditorBegin);
 
+        //cache the current selected entities.
+        ToolsApplicationRequests::Bus::BroadcastResult(m_selectedBeforeStartingGame, &ToolsApplicationRequests::GetSelectedEntities);
+        //deselect entities if selected when entering game mode before deactivating the entities in StartPlayInEditor(...)
+        if (!m_selectedBeforeStartingGame.empty())
+        {
+            ToolsApplicationRequests::Bus::Broadcast(&ToolsApplicationRequests::MarkEntitiesDeselected, m_selectedBeforeStartingGame);
+        }
+
         if (m_isLegacySliceService)
         {
             SliceEditorEntityOwnershipService* editorEntityOwnershipService =
@@ -507,8 +515,6 @@ namespace AzToolsFramework
 
         m_isRunningGame = true;
 
-        ToolsApplicationRequests::Bus::BroadcastResult(m_selectedBeforeStartingGame, &ToolsApplicationRequests::GetSelectedEntities);
-
         EditorEntityContextNotificationBus::Broadcast(&EditorEntityContextNotification::OnStartPlayInEditor);
     }
 

Gems/PhysX/Code/Source/EditorShapeColliderComponent.cpp

@@ -685,11 +685,17 @@ namespace PhysX
     void EditorShapeColliderComponent::OnSelected()
     {
         if (auto* physXSystem = GetPhysXSystem())
+        {
+            if (!m_physXConfigChangedHandler.IsConnected())
             {
                 physXSystem->RegisterSystemConfigurationChangedEvent(m_physXConfigChangedHandler);
+            }
+            if (!m_onDefaultMaterialLibraryChangedEventHandler.IsConnected())
+            {
                 physXSystem->RegisterOnDefaultMaterialLibraryChangedEventHandler(m_onDefaultMaterialLibraryChangedEventHandler);
             }
         }
+    }
 
     void EditorShapeColliderComponent::OnDeselected()
     {

Gems/PhysX/Code/Source/PhysXCharacters/Components/EditorCharacterControllerComponent.cpp

@@ -148,10 +148,13 @@ namespace PhysX
     void EditorCharacterControllerComponent::OnSelected()
     {
         if (auto* physXSystem = GetPhysXSystem())
+        {
+            if (!m_physXConfigChangedHandler.IsConnected())
             {
                 physXSystem->RegisterSystemConfigurationChangedEvent(m_physXConfigChangedHandler);
             }
         }
+    }
 
     void EditorCharacterControllerComponent::OnDeselected()
     {