fix(FEC-12648): Text style configuration is not working

[JonathanTGold]

Description of the Changes

solves: FEC-12648

Findings:

1. by Default, the player uses its own text displayer and not the browser's native one
2. there are two level of text style (in PKTextConfigObject type):

textTrackDisplaySetting: PKTextTrackDisplaySettingObject,
textStyle: PKTextStyleObject,forceCenter: boolean,

3. by default both of them work
4. in case you use the browser native text tracks (useNativeTextTrack set to true) - only textStyle works
5. in case you use Shaka text displayer (useShakaTextTrackDisplay set to true) - none of them work

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