Allow GlobalImageCache.clear to, optionally, only remove the actual data (PR 11912 follow-up)

When "Cleanup" is triggered, you obviously need to remove all globally cached data on *both* the main- and worker-threads.
However, the current the implementation of the `GlobalImageCache.clear` method also means that we lose *all* information about which images were cached and not just their data. This thus has the somewhat unfortunate side-effect of requiring images, which were previously known to be "global", to *again* having to reach `NUM_PAGES_THRESHOLD` before being cached again.

To avoid doing unnecessary parsing after "Cleanup", we can thus let `GlobalImageCache.clear` keep track of which images were cached while still removing their actual data. This should not have any significant impact on memory usage, since the only extra thing being kept is a `RefSetCache` (essentially an Object) with a couple of `Set`s containing only integers.

src/core/document.js

@@ -844,8 +844,10 @@ class PDFDocument {
     return this.catalog.fontFallback(id, handler);
   }
 
-  async cleanup() {
-    return this.catalog ? this.catalog.cleanup() : clearPrimitiveCaches();
+  async cleanup(manuallyTriggered = false) {
+    return this.catalog
+      ? this.catalog.cleanup(manuallyTriggered)
+      : clearPrimitiveCaches();
   }
 }
 

src/core/image_utils.js

@@ -199,8 +199,10 @@ class GlobalImageCache {
     this._imageCache.put(ref, data);
   }
 
-  clear() {
-    this._refCache.clear();
+  clear(onlyData = false) {
+    if (!onlyData) {
+      this._refCache.clear();
+    }
     this._imageCache.clear();
   }
 }

src/core/obj.js

@@ -716,9 +716,9 @@ class Catalog {
     });
   }
 
-  cleanup() {
+  cleanup(manuallyTriggered = false) {
     clearPrimitiveCaches();
-    this.globalImageCache.clear();
+    this.globalImageCache.clear(/* onlyData = */ manuallyTriggered);
     this.pageKidsCountCache.clear();
 
     const promises = [];

src/core/pdf_manager.js

@@ -76,8 +76,8 @@ class BasePdfManager {
     return this.pdfDocument.fontFallback(id, handler);
   }
 
-  cleanup() {
-    return this.pdfDocument.cleanup();
+  cleanup(manuallyTriggered = false) {
+    return this.pdfDocument.cleanup(manuallyTriggered);
   }
 
   async ensure(obj, prop, args) {

src/core/worker.js

@@ -625,7 +625,7 @@ var WorkerMessageHandler = {
     });
 
     handler.on("Cleanup", function wphCleanup(data) {
-      return pdfManager.cleanup();
+      return pdfManager.cleanup(/* manuallyTriggered = */ true);
     });
 
     handler.on("Terminate", function wphTerminate(data) {