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.

src/display/canvas.js

@@ -2157,9 +2157,11 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       this.paintInlineImageXObject(maskCanvas.canvas);
     },
 
-    paintImageMaskXObjectRepeat: function CanvasGraphics_paintImageMaskXObjectRepeat(
+    paintImageMaskXObjectRepeat(
       imgData,
       scaleX,
+      skewX = 0,
+      skewY = 0,
       scaleY,
       positions
     ) {
@@ -2190,7 +2192,14 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
       var ctx = this.ctx;
       for (var i = 0, ii = positions.length; i < ii; i += 2) {
         ctx.save();
-        ctx.transform(scaleX, 0, 0, scaleY, positions[i], positions[i + 1]);
+        ctx.transform(
+          scaleX,
+          skewX,
+          skewY,
+          scaleY,
+          positions[i],
+          positions[i + 1]
+        );
         ctx.scale(1, -1);
         ctx.drawImage(maskCanvas.canvas, 0, 0, width, height, 0, -1, 1, 1);
         ctx.restore();