fix getter of result from Image query cache (facebook#23602)

Summary:
We assume `map` is the type of `Map`, but actually it's not, so we would get type error.

[iOS] [Fixed] - [RNTester] fix getter of result from Image query cache
Pull Request resolved: facebook#23602

Differential Revision: D14221747

Pulled By: cpojer

fbshipit-source-id: 06cf08078a330e4d5731ad72010c87e9e69fcd7b

Author: zhongwuzw

Libraries/Image/Image.android.js

@@ -157,7 +157,7 @@ function abortPrefetch(requestId: number) {
  */
 async function queryCache(
   urls: Array<string>,
-): Promise<Map<string, 'memory' | 'disk'>> {
+): Promise<{[string]: 'memory' | 'disk' | 'disk/memory'}> {
   return await ImageLoader.queryCache(urls);
 }
 

Libraries/Image/Image.ios.js

@@ -48,7 +48,7 @@ function prefetch(url: string) {
 
 async function queryCache(
   urls: Array<string>,
-): Promise<Map<string, 'memory' | 'disk' | 'disk/memory'>> {
+): Promise<{[string]: 'memory' | 'disk' | 'disk/memory'}> {
   return await ImageViewManager.queryCache(urls);
 }
 

RNTester/js/ImageExample.js

@@ -93,7 +93,7 @@ class NetworkImageCallbackExample extends React.Component<
                     `✔ Prefetch OK (+${new Date() - mountTime}ms)`,
                   );
                   Image.queryCache([IMAGE_PREFETCH_URL]).then(map => {
-                    const result = map.get(IMAGE_PREFETCH_URL);
+                    const result = map[IMAGE_PREFETCH_URL];
                     if (result) {
                       this._loadEventFired(
                         `✔ queryCache "${result}" (+${new Date() -