modifier stack: lazy initialize normals

many modifiers were calculating normals, when those normals were ignored by the next modifier.
now flag normals as dirty and recalculate for modifiers that set use `dependsOnNormals()` callback.

Quick test on mesh with 12 modifiers (mostly build type), calculated normals 6 times, now it only runs once - so this will give some speedup too.

source/blender/modifiers/intern/MOD_array.c

@@ -565,11 +565,7 @@ static DerivedMesh *arrayModifier_doArray(ArrayModifierData *amd,
 
 	if ((amd->offset_type & MOD_ARR_OFF_OBJ) && (amd->offset_ob)) {
 		/* Update normals in case offset object has rotation. */
-		
-		/* BMESH_TODO: check if normal recalc needed under any other
-		 * conditions? */
-
-		CDDM_calc_normals(result);
+		result->dirty |= DM_DIRTY_NORMALS;
 	}
 
 	BM_mesh_free(bm);
@@ -591,9 +587,6 @@ static DerivedMesh *applyModifier(ModifierData *md, Object *ob,
 
 	result = arrayModifier_doArray(amd, md->scene, ob, dm, 0);
 
-	//if (result != dm)
-	//	CDDM_calc_normals_mapping(result);
-
 	return result;
 }