enable XMLTextFormatter for application/xml and text/xml

Summary:
Currently in the Flipper network plugin implementation, XMLTextFormatter is only enabled if `content-type` is `text/html`.

We should enable it for `application/xml` and `text/xml` as well.

Reviewed By: mweststrate

Differential Revision: D37733487

fbshipit-source-id: f272c5d0a305cf4afd32701d40459c3e11049886

desktop/plugins/public/network/RequestDetails.tsx

@@ -470,7 +470,11 @@ class XMLTextFormatter {
   }
 
   format(body: string, contentType: string) {
-    if (contentType.startsWith('text/html')) {
+    if (
+      contentType.startsWith('text/html') ||
+      contentType.startsWith('text/xml') ||
+      contentType.startsWith('application/xml')
+    ) {
       return <XMLText body={body} />;
     }
   }