AP.request unable to get correct binary data through Get URI for download attachment API

Issue Summary

Using AP.request to make a call to /wiki/rest/api/content/{id}/child/attachment/{attachmentId}/download, when the attachment is binary data (e.g. an image), results in the response data being incorrect.

This is likely due to the fact that AP.request uses `XMLHttpRequest.responseText`, which overwrites non-ASCII values, thus corrupting any binary attachments.

Note that text attachments work correctly.

Steps to Reproduce

1. Add an image attachment on a page
2. Call the API to get attachments using any means

   GET /rest/api/content/{contentId}/child/attachment
   

1. Note the attachment ID
2. Call the download API using AP.request:

   GET /rest/api/content/{contentId}/child/attachment/{attachmentId}/download
   

Expected Results

AP.request should follow the redirect, and the response should be the correct binary data for the image attachment. One should be able to display the image via

<img src='data:image/jpeg;base64,<base64encoded response> />

Actual Results

The binary data response is incorrect.

Workaround

1. If CORS is not in place (e.g. you wish to embed an image within an <img> tag)

Call either of the following APIs with AP.request:

/rest/api/content/{attachmentId}

/rest/api/content/{containerContentId}?expand=children.attachment

and get the _links.download path of the corresponding attachment. Since the call is made in the browser, one can use this value to construct a URL to download the attachment.

For example,

<img src=<baseURL + downloadURL> />

2. If CORS is in place

Make a request to this API from the Connect app server, then serve the result to the client.