set blob as default XMLHttpRequest header response type if supported (#22063)

Summary:
This is a problem that is discussed in issue #21092

Related issues: #21851 #19717

Found the code to eventually fix this issue [here](899b155746/fetch.js (L486))

- [x] Fetching an image locally and check if the blob is there, as well as its size > 0.

___
Help reviewers and the release process by writing your own release notes. See below for an example.

[GENERAL] [ENHANCEMENT] [whatwg-fetch] - set blob as default XMLHttpRequest header response type if supported
Pull Request resolved: https://github.com/facebook/react-native/pull/22063

Differential Revision: D13408797

Pulled By: cpojer

fbshipit-source-id: 9822d5a7e24bacd72838f3fc9a61b1a97b44484b

Libraries/vendor/core/whatwg-fetch.js

@@ -516,6 +516,10 @@
         xhr.withCredentials = false;
       }
 
+      if ('responseType' in xhr && support.blob) {
+        xhr.responseType = 'blob'
+      }
+
       request.headers.forEach(function(value, name) {
         xhr.setRequestHeader(name, value);
       });