https://github.com/godotengine/godot/blob/master/editor/plugins/sprite_2d_editor_plugin.cpp
That menu comes from there(far as I can tell), starting from line 114:
void Sprite2DEditor::_menu_option(int p_option) {
if (!node) {
return;
}
selected_menu_item = (Menu)p_option;
switch (p_option) {
case MENU_OPTION_CONVERT_TO_MESH_2D: {
debug_uv_dialog->get_ok_button()->set_text(TTR("Create Mesh2D"));
debug_uv_dialog->set_title(TTR("Mesh2D Preview"));
_update_mesh_data();
debug_uv_dialog->popup_centered();
debug_uv->update();
} break;
case MENU_OPTION_CONVERT_TO_POLYGON_2D: {
debug_uv_dialog->get_ok_button()->set_text(TTR("Create Polygon2D"));
debug_uv_dialog->set_title(TTR("Polygon2D Preview"));
_update_mesh_data();
debug_uv_dialog->popup_centered();
debug_uv->update();
} break;
case MENU_OPTION_CREATE_COLLISION_POLY_2D: {
debug_uv_dialog->get_ok_button()->set_text(TTR("Create CollisionPolygon2D"));
debug_uv_dialog->set_title(TTR("CollisionPolygon2D Preview"));
_update_mesh_data();
debug_uv_dialog->popup_centered();
debug_uv->update();
} break;
case MENU_OPTION_CREATE_LIGHT_OCCLUDER_2D: {
debug_uv_dialog->get_ok_button()->set_text(TTR("Create LightOccluder2D"));
debug_uv_dialog->set_title(TTR("LightOccluder2D Preview"));
_update_mesh_data();
debug_uv_dialog->popup_centered();
debug_uv->update();
} break;
}
}