Change test-case issue4914 to an annotations test

This PDF file (see issue 4914) originally regressed in PR 4318, and was subsequently fixed in PR 4915.

I added the PDF file as a (linked) test-case in PR 6481, in an effort to prevent regressions. Since we at that time didn't have the necessary framework in place, in order to correctly test annotations, this almost regressed *again* in PR mozilla#6672 (comment).

In that PDF file, some of the annotations are both printable and hidden, and should definitely *not* be visible on normal display. Hence this patch, which adds the `annotations` flag to the manifest in order to ensure that those annotations won't be rendered when `intent === 'display'`.

test/test_manifest.json

@@ -498,6 +498,7 @@
        "link": true,
        "lastPage": 1,
        "type": "eq",
+       "annotations": true,
        "about": "PDF with annotations, some of which have the Hidden flag set."
     },
     {  "id": "issue4665-text",