Hi Steve,
Did you try "Insert Menu Item"? Create a new action, stop the recording, leave it selected, and then in the Action Panel flyout, select "Insert Menu Item…"? It should show a dialog that no menu item is selected. Then go to Select> All Layers, and that should replace ‘None Selected’ in the Insert Menu Item dialog. Now hit OK and you should have the generic Select all layers action you want.
Of course you’ll probably want to just incorporate the Insert Menu Item is an existing action you already have created. The above steps just give you the simplified example.