fix(core): re-export AmplifyServerContextError from internals/adapter-core path

Ensures the old import path via @aws-amplify/core/internals/adapter-core
still provides AmplifyServerContextError.

Author: bobbor

packages/core/src/adapterCore/index.ts

@@ -2,3 +2,4 @@
 // SPDX-License-Identifier: Apache-2.0
 
 export { CookieStorage, KeyValueStorageMethodValidator } from './serverContext';
+export { AmplifyServerContextError } from '../errors/AmplifyServerContextError';