Convert Metadata to use private class fields

Please refer to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/Private_class_fields

src/display/metadata.js

@@ -16,25 +16,29 @@
 import { objectFromMap } from "../shared/util.js";
 
 class Metadata {
+  #metadataMap;
+
+  #data;
+
   constructor({ parsedData, rawData }) {
-    this._metadataMap = parsedData;
-    this._data = rawData;
+    this.#metadataMap = parsedData;
+    this.#data = rawData;
   }
 
   getRaw() {
-    return this._data;
+    return this.#data;
   }
 
   get(name) {
-    return this._metadataMap.get(name) ?? null;
+    return this.#metadataMap.get(name) ?? null;
   }
 
   getAll() {
-    return objectFromMap(this._metadataMap);
+    return objectFromMap(this.#metadataMap);
   }
 
   has(name) {
-    return this._metadataMap.has(name);
+    return this.#metadataMap.has(name);
   }
 }