Improve global image caching for small images (PR 11912 follow-up, issue 12098)

When implementing the `GlobalImageCache` functionality I was mostly worried about the effect of *very large* images, hence the maximum number of cached images were purposely kept quite low[1].
However, there's one fairly obvious problem with that approach: In documents with hundreds, or even thousands, of *small* images the `GlobalImageCache` as implemented becomes essentially pointless.

Hence this patch, where the `GlobalImageCache`-implementation is changed in the following ways:
 - We're still guaranteed to be able to cache a *minimum* number of images, set to `10` (similar as before).
 - If the *total* size of all the cached image data is below a threshold[2], we're allowed to cache additional images.

This patch thus *improve*, but doesn't completely fix, issue 12098. Note that that document is created by a *very poor* PDF generator, since every single page contains the *entire* document (with all of its /Resources) and to create the individual pages clipping is used.[3]

---
[1] Currently set to `10` images; imagine what would happen to overall memory usage if we encountered e.g. 50 images each 10 MB in size.

[2] This value was chosen, somewhat randomly, to be `40` megabytes; basically five times the [maximum individual image size per page](6249ef517d/src/display/api.js (L2483-L2484)).

[3] This surely has to be some kind of record w.r.t. how badly PDF generators can mess things up...

src/core/evaluator.js

@@ -609,6 +609,9 @@ class PartialEvaluator {
       .then(imageObj => {
         imgData = imageObj.createImageData(/* forceRGBA = */ false);
 
+        if (cacheKey && imageRef && cacheGlobally) {
+          this.globalImageCache.addByteSize(imageRef, imgData.data.length);
+        }
         return this._sendImgData(objId, imgData, cacheGlobally);
       })
       .catch(reason => {
@@ -633,6 +636,7 @@ class PartialEvaluator {
             objId,
             fn: OPS.paintImageXObject,
             args,
+            byteSize: 0, // Temporary entry, note `addByteSize` above.
           });
         }
       }