[LYN-3272] Added API for retrieving the number of selected entities. Updated InfoBar to use this new API.

Code/Framework/AzToolsFramework/AzToolsFramework/API/ToolsApplicationAPI.h

@@ -348,6 +348,11 @@ namespace AzToolsFramework
          */
         virtual bool AreAnyEntitiesSelected() = 0;
 
+        /*!
+         * Returns the number of selected entities.
+         */
+        virtual int GetSelectedEntitiesCount() = 0;
+
         /*!
          * Retrieves the set of selected entities.
          * \return a list of entity Ids.

Code/Framework/AzToolsFramework/AzToolsFramework/Application/ToolsApplication.cpp

@@ -395,6 +395,7 @@ namespace AzToolsFramework
                 ->Event("MarkEntityDeselected", &ToolsApplicationRequests::MarkEntityDeselected)
                 ->Event("IsSelected", &ToolsApplicationRequests::IsSelected)
                 ->Event("AreAnyEntitiesSelected", &ToolsApplicationRequests::AreAnyEntitiesSelected)
+                ->Event("GetSelectedEntitiesCount", &ToolsApplicationRequests::GetSelectedEntitiesCount)
                 ;
 
             behaviorContext->EBus<ToolsApplicationNotificationBus>("ToolsApplicationNotificationBus")

Code/Framework/AzToolsFramework/AzToolsFramework/Application/ToolsApplication.h

@@ -101,6 +101,7 @@ namespace AzToolsFramework
         SourceControlFileInfo GetSceneSourceControlInfo() override;
 
         bool AreAnyEntitiesSelected() override { return !m_selectedEntities.empty(); }
+        int GetSelectedEntitiesCount() override { return m_selectedEntities.size(); }
         const EntityIdList& GetSelectedEntities() override { return m_selectedEntities; }
         const EntityIdList& GetHighlightedEntities() override { return m_highlightedEntities; }
         void SetSelectedEntities(const EntityIdList& selectedEntities) override;