fix(FEC-11655): System highlights 2 options (captions) after clicking the "Change media" button on Safari

[JonathanTGold]

Description of the Changes

issue: look at _getParsedTextTracks() on https://github.com/kaltura/playkit-js/blob/master/src/engines/html5/media-source/adapters/native-adapter.js#L696
when this method called at the second time (like after calling changeMedie() in this case) the textTracks including the external text trcak.

and the first condition evaluates to false and therefore the indexes start from 1 instead of 0 which leads to an incorrect index value (that is - same index for two different tracks) on the getExternalTracks() method in (https://github.com/kaltura/playkit-js/blob/master/src/track/external-captions-handler.js#L118) since it is relying on the textTracks.langth.

and that bring the method the _markActiveTrack(track: Track) method on https://github.com/kaltura/playkit-js/blob/master/src/player.js#L2414 to mark both tracks as active

fix: in the native adapter not relying on the for index which progresses regardless of actual track index

solves: FEC-11655

CheckLists

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• test are passing in local environment
• Travis tests are passing (or test results are not worse than on master branch :))
• Docs have been updated

[RoyBregman]

Please fix Title to "fix(FEC-11655):..."
Besides that LGTM

[Yuvalke]

@JonathanTGold u can change the naming from index to native_text_track_index something more meaningful 👍