[Flight] Move bundler configs to use Suspense instead of returning thenable (#18367)

* Move bundler configs to use suspense instead of returning thenable

* Fix some Flow types

scripts/flow/environment.js

@@ -67,5 +67,9 @@ declare module 'EventListener' {
   };
 }
 
-declare function __webpack_chunk_load__(id: string): {then(() => mixed): mixed};
+type Thenable = {
+  then(resolve: (mixed) => mixed, reject?: (Error) => mixed): Thenable,
+};
+
+declare function __webpack_chunk_load__(id: string): Thenable;
 declare function __webpack_require__(id: string): {default: any};

scripts/flow/react-relay-hooks.js

@@ -15,11 +15,6 @@ type JSONValue =
   | {[key: string]: JSONValue}
   | Array<JSONValue>;
 
-type Thenable = {
-  then(resolve: () => mixed, reject: (error: Error) => mixed): mixed,
-  ...
-};
-
 declare module 'ReactFlightDOMRelayServerIntegration' {
   declare export opaque type Destination;
   declare export function emitModel(
@@ -43,7 +38,7 @@ declare module 'ReactFlightDOMRelayServerIntegration' {
 }
 
 declare module 'ReactFlightDOMRelayClientIntegration' {
-  declare export opaque type ModuleReference;
+  declare export opaque type ModuleReference<T>;
   declare export opaque type ModuleMetaData;
   declare export function resolveModuleReference<T>(
     moduleData: ModuleMetaData,
@@ -51,9 +46,6 @@ declare module 'ReactFlightDOMRelayClientIntegration' {
   declare export function preloadModule<T>(
     moduleReference: ModuleReference<T>,
   ): void;
-  declare export function loadModule<T>(
-    moduleReference: ModuleReference<T>,
-  ): null | Thenable;
   declare export function requireModule<T>(
     moduleReference: ModuleReference<T>,
   ): T;