refactor(packages): change package structure

packages/system/src/index.ts

@@ -1,4 +1,6 @@
+export * from './constants';
 export * from './types';
-export { errorMessages } from './constants';
-
-export const internalsSymbol = Symbol.for('internals');
+export * from './utils';
+export * from './xydrag';
+export * from './xyhandle';
+export * from './xypanzoom';