Update all Object.fromEntries call-sites to ensure that a null pr…

…ototype is used

Given that `Object.fromEntries` doesn't seem to *guarantee* that a `null` prototype is used, we thus hack around that by using `Object.assign` with `Object.create(null)`.

src/display/annotation_storage.js

@@ -13,6 +13,8 @@
  * limitations under the License.
  */
 
+import { objectFromEntries } from "../shared/util.js";
+
 /**
  * Key/value storage for annotation data in forms.
  */
@@ -67,7 +69,7 @@ class AnnotationStorage {
     if (this._storage.size === 0) {
       return null;
     }
-    return Object.fromEntries(this._storage);
+    return objectFromEntries(this._storage);
   }
 
   get size() {

src/display/metadata.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import { assert } from "../shared/util.js";
+import { assert, objectFromEntries } from "../shared/util.js";
 import { SimpleXMLParser } from "../shared/xml_parser.js";
 
 class Metadata {
@@ -118,7 +118,7 @@ class Metadata {
   }
 
   getAll() {
-    return Object.fromEntries(this._metadataMap);
+    return objectFromEntries(this._metadataMap);
   }
 
   has(name) {

src/display/optional_content_config.js

@@ -12,7 +12,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { warn } from "../shared/util.js";
+import { objectFromEntries, warn } from "../shared/util.js";
 
 class OptionalContentGroup {
   constructor(name, intent) {
@@ -145,7 +145,7 @@ class OptionalContentConfig {
     if (!this._groups.size) {
       return null;
     }
-    return Object.fromEntries(this._groups);
+    return objectFromEntries(this._groups);
   }
 
   getGroup(id) {