Allow generator actions to affect children

Changing the generator will often modify the underlying children's
properties.  We should store these data in the stack.  Also add the
ability to change layers

Fixes https://gitlab.com/kicad/code/kicad/-/issues/21476

pcbnew/generators/pcb_tuning_pattern.cpp

@@ -25,6 +25,7 @@
 #include <pcb_generator.h>
 #include <generators_mgr.h>
 
+#include <functional>
 #include <optional>
 #include <magic_enum.hpp>
 
@@ -358,6 +359,14 @@ public:
         }
     }
 
+    void SetLayer( PCB_LAYER_ID aLayer ) override
+    {
+        PCB_GENERATOR::SetLayer( aLayer );
+
+        RunOnChildren( [aLayer]( BOARD_ITEM* item ) { item->SetLayer( aLayer ); },
+                       RECURSE_MODE::RECURSE );
+    }
+
     const BOX2I GetBoundingBox() const override
     {
         return getOutline().BBox();