Make startFlowing explicit in Flight

This is already an explicit call in Fizz. This moves flowing to be explicit.

That way we can avoid calling it in start() for web streams and therefore
avoid the reentrant call.

packages/react-noop-renderer/src/ReactNoopFlightServer.js

@@ -68,6 +68,7 @@ function render(model: ReactModel, options?: Options): Destination {
     options ? options.onError : undefined,
   );
   ReactNoopFlightServer.startWork(request);
+  ReactNoopFlightServer.startFlowing(request);
   return destination;
 }
 

packages/react-server-dom-relay/src/ReactFlightDOMRelayServer.js

@@ -13,7 +13,11 @@ import type {
   Destination,
 } from './ReactFlightDOMRelayServerHostConfig';
 
-import {createRequest, startWork} from 'react-server/src/ReactFlightServer';
+import {
+  createRequest,
+  startWork,
+  startFlowing,
+} from 'react-server/src/ReactFlightServer';
 
 type Options = {
   onError?: (error: mixed) => void,
@@ -32,6 +36,7 @@ function render(
     options ? options.onError : undefined,
   );
   startWork(request);
+  startFlowing(request);
 }
 
 export {render};

packages/react-server-native-relay/src/ReactFlightNativeRelayServer.js

@@ -13,7 +13,11 @@ import type {
   Destination,
 } from './ReactFlightNativeRelayServerHostConfig';
 
-import {createRequest, startWork} from 'react-server/src/ReactFlightServer';
+import {
+  createRequest,
+  startWork,
+  startFlowing,
+} from 'react-server/src/ReactFlightServer';
 
 function render(
   model: ReactModel,
@@ -22,6 +26,7 @@ function render(
 ): void {
   const request = createRequest(model, destination, config);
   startWork(request);
+  startFlowing(request);
 }
 
 export {render};

packages/react-server/src/ReactFlightServer.js

@@ -763,7 +763,6 @@ function flushCompletedChunks(request: Request): void {
 }
 
 export function startWork(request: Request): void {
-  request.flowing = true;
   scheduleWork(() => performWork(request));
 }