Improve performance with image masks (bug 857031)

- it aims to partially fix performance issue reported: https://bugzilla.mozilla.org/show_bug.cgi?id=857031;
- the idea is too avoid to use byte arrays but use ImageBitmap which are a way faster to draw:
  * an ImageBitmap is Transferable which means that it can be built in the worker instead of in the main thread:
    - this is achieved in using an OffscreenCanvas when it's available, there is a bug to enable them
      for pdf.js: https://bugzilla.mozilla.org/show_bug.cgi?id=1763330;
    - or in using createImageBitmap: in Firefox a task is sent to the main thread to build the bitmap so
      it's slightly slower than using an OffscreenCanvas.
  * it's transfered from the worker to the main thread by "reference";
  * the byte buffers used to create the image data have a very short lifetime and ergo the memory used is globally
    less than before.
- Use the localImageCache for the mask;
- Fix the pdf issue4436r.pdf: it was expected to have a binary stream for the image;
- Move the singlePixel trick from operator_list to image: this way we can use this trick even if it isn't in a set
  as defined in operator_list.

test/test.js

@@ -959,6 +959,8 @@ async function startBrowser(browserName, startUrl = "") {
       print_printer: "PDF",
       "print.printer_PDF.print_to_file": true,
       "print.printer_PDF.print_to_filename": printFile,
+      // Enable OffscreenCanvas
+      "gfx.offscreencanvas.enabled": true,
     };
   }
 

test/test_manifest.json

@@ -5576,7 +5576,7 @@
     },
     {  "id": "issue4436",
        "file": "pdfs/issue4436r.pdf",
-       "md5": "4e43d692d213f56674fcac92110c7364",
+       "md5": "f5dc60cce342ac8d165069a80d23b92e",
        "rounds": 1,
        "link": false,
        "type": "eq"

test/unit/api_spec.js

@@ -1666,7 +1666,7 @@ describe("api", function () {
 
       expect(fingerprints1).not.toEqual(fingerprints2);
 
-      expect(fingerprints1).toEqual(["2f695a83d6e7553c24fc08b7ac69712d", null]);
+      expect(fingerprints1).toEqual(["657428c0628e329f9a281fb6d2d092d4", null]);
       expect(fingerprints2).toEqual(["04c7126b34a46b6d4d6e7a1eff7edcb6", null]);
 
       await Promise.all([loadingTask1.destroy(), loadingTask2.destroy()]);