Use setTimeout to schedule work on the server in Edge environments (#26348)

We rely heavily on being able to batch rendering after multiple fetches
etc. have completed on the server. However, we only do this in the
Node.js build. Node.js `setImmediate` has the exact semantics we need.
To be after the current cycle of I/O so that we can collect after all
those I/O events already in the queue has been processed.

This doesn't exist in standard browsers, so we ended up not using it
there. We could've used `setTimeout` but that risks being throttled
which would severely negatively affect the performance so we just did it
synchronously there. We probably could just use the `scheduler` there.

Now we have a separate build for Edge where `setTimeout(..., 0)`
actually behaves like `setImmediate` which is what we want. So we can
just use that in that build.

@Jarred-Sumner not sure what you want for Bun.

packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMEdge-test.js

@@ -15,6 +15,10 @@ global.ReadableStream =
 global.TextEncoder = require('util').TextEncoder;
 global.TextDecoder = require('util').TextDecoder;
 
+// Don't wait before processing work on the server.
+// TODO: we can replace this with FlightServer.act().
+global.setTimeout = cb => cb();
+
 let clientExports;
 let webpackMap;
 let webpackModules;

packages/react-server/src/ReactServerStreamConfigEdge.js

@@ -13,7 +13,7 @@ export type PrecomputedChunk = Uint8Array;
 export opaque type Chunk = Uint8Array;
 
 export function scheduleWork(callback: () => void) {
-  callback();
+  setTimeout(callback, 0);
 }
 
 export function flushBuffered(destination: Destination) {

packages/react/src/__tests__/ReactFetchEdge-test.js

@@ -20,6 +20,10 @@ global.Response = require('node-fetch').Response;
 // Patch for Edge environments for global scope
 global.AsyncLocalStorage = require('async_hooks').AsyncLocalStorage;
 
+// Don't wait before processing work on the server.
+// TODO: we can replace this with FlightServer.act().
+global.setTimeout = cb => cb();
+
 let fetchCount = 0;
 async function fetchMock(resource, options) {
   fetchCount++;