fix(chapters): removed duplicate chapters by id (shaka-project#4810)

fixes shaka-project#4750

Solved by creating a `Set` for filtering out deplicate elements.

Need confirmation, Shouldn't we add an `assert` for `language` argument
passed to
https://github.com/shaka-project/shaka-player/blob/76f96b9fee2dc43b03f6803dd80c51fdc5b73a9e/lib/player.js#L4340-L4342

AUTHORS

@@ -68,6 +68,7 @@ Prakash <duggaraju@gmail.com>
 Robert Colantuoni <rgc@colantuoni.com>
 Robert Galluccio <robertnw5@gmail.com>
 Rodolphe Breton <robloche@gmail.com>
+Rohan Gupta <rohangupta1528@gmail.com>
 Roi Lipman <roilipman@gmail.com>
 Roksolana Ivanyshyn <roksolana.ivanyshyn.pub@gmail.com>
 Rostislav Hejduk <Ross-cz@users.noreply.github.com>

CONTRIBUTORS

@@ -100,6 +100,7 @@ Robert Colantuoni <rgc@colantuoni.com>
 Robert Galluccio <robertnw5@gmail.com>
 Rodolphe Breton <robloche@gmail.com>
 Rohit Makasana <rohitbm@google.com>
+Rohan Gupta <rohangupta1528@gmail.com>
 Roi Lipman <roilipman@gmail.com>
 Roksolana Ivanyshyn <roksolana.ivanyshyn.pub@gmail.com>
 Rostislav Hejduk <Ross-cz@users.noreply.github.com>

lib/player.js

@@ -4347,6 +4347,7 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
       return [];
     }
     const chapters = [];
+    const uniqueChapters = new Set();
     for (const chaptersTrack of chaptersTracksWithLanguage) {
       if (chaptersTrack && chaptersTrack.cues) {
         for (const cue of chaptersTrack.cues) {
@@ -4361,7 +4362,10 @@ shaka.Player = class extends shaka.util.FakeEventTarget {
             startTime: cue.startTime,
             endTime: cue.endTime,
           };
-          chapters.push(chapter);
+          if (!uniqueChapters.has(id)) {
+            chapters.push(chapter);
+            uniqueChapters.add(id);
+          }
         }
       }
     }