Tweak the QueueOptimizer to recognize OPS.paintImageMaskXObject operators as *repeated* when the "skew" transformation matrix elements are non-zero (issue 8078)

*First of all, I should mention that my understanding of the finer details of the `QueueOptimizer` (and its related `CanvasGraphics` methods) is somewhat limited.*
Hence I'm not sure if there's actually a very good reason for *only* considering ImageMasks where the "skew" transformation matrix elements are zero as *repeated*, however simply looking at the code I just don't see why these elements cannot be non-zero as long as they are *all identical* for the ImageMasks.
Furthermore, looking at the *group* case (which is what we're currently falling back to), there's no particular limitation placed upon the transformation matrix elements.

While this patch obviously isn't enough to *completely* fix the issue, since there should be a visible Pattern rendered as well[1], it seem (at least to me) like enough of an improvement that submitting this is justified.
With these changes the referenced PDF document will no longer hang the *entire* browser, and rendering also finishes in a *reasonable* time (< 10 seconds for me) which seem fine given the *huge* number of identical inline images present.[2]

---
[1] Temporarily changing the Pattern to a solid color *does* render the correct/expected area, which suggests that the remaining problem is a pre-existing issue related to the Pattern-handling itself rather than the `QueueOptimizer` functionality.

[2] The document isn't exactly rendered immediately in e.g. Adobe Reader either.

test/pdfs/issue8078.pdf.link

@@ -0,0 +1 @@
+https://bugs.ghostscript.com/attachment.cgi?id=7455

test/test_manifest.json

@@ -711,6 +711,14 @@
        "type": "eq",
        "about": "Type1 font with |Ref|s in the Differences array of the Encoding dictionary."
     },
+    {  "id": "issue8078",
+       "file": "pdfs/issue8078.pdf",
+       "md5": "8b7d74bc24b4157393e4e88a511c05f1",
+       "link": true,
+       "rounds": 1,
+       "lastPage": 1,
+       "type": "eq"
+    },
     {  "id": "issue8092",
        "file": "pdfs/issue8092.pdf",
        "md5": "e4f3376b35fd132580246c3db1fbd738",