Add find_surface_nodes_in_area LUA call which permit to only get the nodes which touch air. This permit to massively improve performance for mods like plantlife

src/script/lua_api/l_env.h

@@ -119,6 +119,10 @@ class ModApiEnvMod : public ModApiBase {
 	// nodenames: eg. {"ignore", "group:tree"} or "default:dirt"
 	static int l_find_nodes_in_area(lua_State *L);
 
+	// find_surface_nodes_in_area(minp, maxp, nodenames) -> list of positions
+	// nodenames: eg. {"ignore", "group:tree"} or "default:dirt"
+	static int l_find_surface_nodes_in_area(lua_State *L);
+
 	// delete_area(p1, p2) -> true/false
 	static int l_delete_area(lua_State *L);