[meta-only] Move ReactServerStreamConfigFB to react-server from react-server-dom-fb (facebook#27544)

Code organization PR.

It looks like the `ReactServerStreamConfigFB` is only used in the
`relay-server` package. This PR moves it to `react-server` from
`react-server-dom-fb` (similar to how we have config for bun, for
example). This avoids cross-package imports from `react-server` to
`react-server-dom-fb.`

Author: alunyov

packages/react-server-dom-fb/src/ReactServerStreamConfigFB.js renamed to packages/react-server/src/ReactServerStreamConfigFB.js

@@ -84,4 +84,4 @@ export function closeWithError(destination: Destination, error: mixed): void {
   destination.error = error;
 }
 
-export {createFastHashJS as createFastHash} from 'react-server/src/createFastHashJS';
+export {createFastHashJS as createFastHash} from './createFastHashJS';

packages/react-server/src/forks/ReactServerStreamConfig.dom-fb.js

@@ -7,4 +7,4 @@
  * @flow
  */
 
-export * from '../../../react-server-dom-fb/src/ReactServerStreamConfigFB';
+export * from '../ReactServerStreamConfigFB';