Address code and flowtype issues

Author: kidroca

packages/react-native-web/src/exports/Image/index.js

@@ -266,8 +266,12 @@ const Image: React.AbstractComponent<
       updateState(LOADING);
       if (onLoadStart) onLoadStart();
 
+      let headers;
+      if (source && typeof source.headers === 'object')
+        headers = ((source.headers: any): { [key: string]: string });
+
       const requestId = ImageLoader.load(
-        { uri, headers: source?.headers },
+        { uri, headers },
         function load(result) {
           updateState(LOADED);
           setLoadedUri(result.uri);

packages/react-native-web/src/modules/ImageLoader/index.js

@@ -93,7 +93,7 @@ const ImageLoader = {
   ) {
     let complete = false;
     const interval = setInterval(callback, 16);
-    const requestId = ImageLoader.load(uri, callback, errorCallback);
+    const requestId = ImageLoader.load({ uri }, callback, errorCallback);
 
     function callback() {
       const { image } = requests[requestId] || {};
@@ -182,7 +182,7 @@ const ImageLoader = {
   prefetch(uri: string): Promise<void> {
     return new Promise((resolve, reject) => {
       ImageLoader.load(
-        uri,
+        { uri },
         () => {
           // Add the uri to the cache so it can be immediately displayed when used
           // but also immediately remove it to correctly reflect that it has no active references
@@ -205,7 +205,7 @@ const ImageLoader = {
   }
 };
 
-type ImageSource = { uri: string, headers?: Record<string, string> };
+type ImageSource = { uri: string, headers?: { [key: string]: string } };
 
 type ImageResult = {
   uri: string,