[api-minor] Generate images in the worker instead of the main thread.

We introduced the use of OffscreenCanvas in #14754 and this patch aims
to use them for all kind of images.
It'll slightly improve performances (and maybe slightly decrease memory use).
Since an image can be rendered in using some transfer maps but because of
OffscreenCanvas we don't have the underlying pixels array the transfer maps
stuff is re-implemented in using the SVG filter feComponentTransfer.

src/core/evaluator.js

@@ -716,7 +716,12 @@ class PartialEvaluator {
       });
       // We force the use of RGBA_32BPP images here, because we can't handle
       // any other kind.
-      imgData = imageObj.createImageData(/* forceRGBA = */ true);
+      imgData = imageObj.createImageData(
+        /* forceRGBA = */ true,
+        /* isOffscreenCanvasSupported = */ false
+      );
+      operatorList.isOffscreenCanvasSupported =
+        this.options.isOffscreenCanvasSupported;
       operatorList.addImageOps(
         OPS.paintInlineImageXObject,
         [imgData],
@@ -756,11 +761,22 @@ class PartialEvaluator {
       localColorSpaceCache,
     })
       .then(imageObj => {
-        imgData = imageObj.createImageData(/* forceRGBA = */ false);
+        imgData = imageObj.createImageData(
+          /* forceRGBA = */ false,
+          /* isOffscreenCanvasSupported = */ this.options
+            .isOffscreenCanvasSupported
+        );
 
         if (cacheKey && imageRef && cacheGlobally) {
-          this.globalImageCache.addByteSize(imageRef, imgData.data.length);
+          let length = 0;
+          if (imgData.bitmap) {
+            length = imgData.width * imgData.height * 4;
+          } else {
+            length = imgData.data.length;
+          }
+          this.globalImageCache.addByteSize(imageRef, length);
         }
+
         return this._sendImgData(objId, imgData, cacheGlobally);
       })
       .catch(reason => {