fix(chapters): removed duplicate chapters by id

[WINOFFRG]

fixes #4750

Solved by creating a Set for filtering out deplicate elements.

Need confirmation, Shouldn't we add an assert for language argument passed to

shaka-player/lib/player.js

Lines 4340 to 4342 in 76f96b9

	getChapters(language) {
	const LanguageUtils = shaka.util.LanguageUtils;
	const inputlanguage = LanguageUtils.normalize(language);

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[github-actions]

Incremental code coverage: 100.00%

[joeyparrish]

Shouldn't we add an assert for language argument passed to
getChapters(language) {

I don't know what you mean by that. What assertion do you want to add?

Assertions are removed in production builds, and are generally only used in this project to catch mistaken internal assumptions or to manage nullability checks at the compiler level.

[joeyparrish]

Looks good to me, but I'll give @avelad a chance to take a look, too. I'll merge it Monday morning if there are no other comments. (My work-week will be over in a few hours.)

[avelad]

I’ll review it tomorrow