Move the ImageBitmap clean-up into the PDFObjects class

With upcoming changes we'll potentially start to cache `ImageBitmap` data at the document-level, in addition to just at the page-level.
Hence we need to ensure that such data is actually released on clean-up, and rather than duplicating the existing *manual* handling this code is instead moved into the `PDFObjects.clear` method. (In my opinion, this is an overall improvement even without globally cached `ImageBitmap` data.)

*Please note:* This patch is written using the GitHub UI, since I'm currently without a dev machine, so hopefully it's correct and makes sense.

src/display/api.js

@@ -1282,8 +1282,6 @@ class PDFPageProxy {
     this.commonObjs = transport.commonObjs;
     this.objs = new PDFObjects();
 
-    this._bitmaps = new Set();
-
     this.cleanupAfterRender = false;
     this.pendingCleanup = false;
     this._intentStates = new Map();
@@ -1679,10 +1677,6 @@ class PDFPageProxy {
       }
     }
     this.objs.clear();
-    for (const bitmap of this._bitmaps) {
-      bitmap.close();
-    }
-    this._bitmaps.clear();
     this.pendingCleanup = false;
     return Promise.all(waitOn);
   }
@@ -1718,10 +1712,6 @@ class PDFPageProxy {
     if (resetStats && this._stats) {
       this._stats = new StatTimer();
     }
-    for (const bitmap of this._bitmaps) {
-      bitmap.close();
-    }
-    this._bitmaps.clear();
     this.pendingCleanup = false;
     return true;
   }
@@ -2774,9 +2764,8 @@ class WorkerTransport {
           if (imageData) {
             let length;
             if (imageData.bitmap) {
-              const { bitmap, width, height } = imageData;
+              const { width, height } = imageData;
               length = width * height * 4;
-              pageProxy._bitmaps.add(bitmap);
             } else {
               length = imageData.data?.length || 0;
             }
@@ -3150,6 +3139,10 @@ class PDFObjects {
   }
 
   clear() {
+    for (const objId in this.#objs) {
+      const { data } = this.#objs[objId];
+      data?.bitmap?.close(); // Release any `ImageBitmap` data.
+    }
     this.#objs = Object.create(null);
   }
 }