chore: Stop using "Object" in DV codecs mapping (#7946)

Related to #1672

lib/util/stream_utils.js

@@ -461,15 +461,15 @@ shaka.util.StreamUtils = class {
    * @param {!Array<!shaka.extern.Variant>} variants
    */
   static overrideDolbyVisionCodecs(variants) {
-    /** @type {!Object<string, string>} */
-    const codecMap = {
-      'dvav': 'avc3',
-      'dva1': 'avc1',
-      'dvhe': 'hev1',
-      'dvh1': 'hvc1',
-      'dvc1': 'vvc1',
-      'dvi1': 'vvi1',
-    };
+    /** @type {!Map<string, string>} */
+    const codecMap = new Map()
+        .set('dvav', 'avc3')
+        .set('dva1', 'avc1')
+        .set('dvhe', 'hev1')
+        .set('dvh1', 'hvc1')
+        .set('dvc1', 'vvc1')
+        .set('dvi1', 'vvi1');
+
     /** @type {!Set<!shaka.extern.Stream>} */
     const streams = new Set();
     for (const variant of variants) {
@@ -478,9 +478,9 @@ shaka.util.StreamUtils = class {
       }
     }
     for (const video of streams) {
-      for (const dvCodec of Object.keys(codecMap)) {
+      for (const [dvCodec, replacement] of codecMap) {
         if (video.codecs.includes(dvCodec)) {
-          video.codecs = video.codecs.replace(dvCodec, codecMap[dvCodec]);
+          video.codecs = video.codecs.replace(dvCodec, replacement);
           break;
         }
       }