Implement Flight CacheSignal

Notably this is currently always creating a new signal rather than passing
the one you pass into the Web Streams APIs.

It might be better ot pass the original one through so that it can contain
other information such as TaskSignal to handle priorities. However, I'm not
sure if we'd want to wrap it with our own TaskSignal yet.

packages/react-server/src/ReactFlightServer.js

@@ -419,6 +419,7 @@ export type Request = {
   destination: null | Destination,
   bundlerConfig: ClientManifest,
   cache: Map<Function, mixed>,
+  cacheController: AbortController,
   nextChunkId: number,
   pendingChunks: number,
   hints: Hints,
@@ -529,6 +530,7 @@ function RequestInstance(
   this.destination = null;
   this.bundlerConfig = bundlerConfig;
   this.cache = new Map();
+  this.cacheController = new AbortController();
   this.nextChunkId = 0;
   this.pendingChunks = 0;
   this.hints = hints;
@@ -604,7 +606,7 @@ export function createRequest(
   model: ReactClientValue,
   bundlerConfig: ClientManifest,
   onError: void | ((error: mixed) => ?string),
-  identifierPrefix?: string,
+  identifierPrefix: void | string,
   onPostpone: void | ((reason: string) => void),
   temporaryReferences: void | TemporaryReferenceSet,
   environmentName: void | string | (() => string), // DEV-only
@@ -636,7 +638,7 @@ export function createPrerenderRequest(
   onAllReady: () => void,
   onFatalError: () => void,
   onError: void | ((error: mixed) => ?string),
-  identifierPrefix?: string,
+  identifierPrefix: void | string,
   onPostpone: void | ((reason: string) => void),
   temporaryReferences: void | TemporaryReferenceSet,
   environmentName: void | string | (() => string), // DEV-only
@@ -4922,6 +4924,7 @@ export function abort(request: Request, reason: mixed): void {
     if (request.status <= OPEN) {
       request.status = ABORTING;
     }
+    request.cacheController.abort(reason);
     const abortableTasks = request.abortableTasks;
     if (abortableTasks.size > 0) {
       if (enableHalt && request.type === PRERENDER) {

packages/react-server/src/flight/ReactFlightAsyncDispatcher.js

@@ -32,6 +32,10 @@ export const DefaultAsyncDispatcher: AsyncDispatcher = ({
     return entry;
   },
   cacheSignal(): null | AbortSignal {
+    const request = resolveRequest();
+    if (request) {
+      return request.cacheController.signal;
+    }
     return null;
   },
 }: any);