Simplify import usage by exporting from current entry points

[alex-yau-ttd]

Before

import { UID2 } from "@uid2/uid2-sdk";
import { EventType, Uid2CallbackHandler} from "@uid2/uid2-sdk/lib/src/uid2CallbackManager";
import { CallbackContainer } from '@uid2/uid2-sdk/lib/src/sdkBase';

After

import { EventType, UID2, Uid2CallbackHandler, UID2StorageManager } from '@uid2/uid2-sdk';
// AND the above still works, to preserve backward compatibility.