fix: improve types and allow augmentation

[barlock]

Description

Fix a few types in player and plugin and allow typescript module augmentation so plugins can modify the players type as expected.

Specific Changes proposed

For type fixes, I used similar patterns found elsewhere in the codebase, just applied following the same pattern. For module augmentation, this pattern should be used:

declare module 'video.js/dist/types/player' {
    // videojs-contrib-quality-levels
    qualityLevels: {
      VERSION: string;
      (): QualityLevelList;
    };
  }
}

Ideally one wouldn't need to reach into dist but I'm unable to do that without created a named export of Player on video.js which I didn't think was wanted. Happy to make the change though. JSDoc seems to prevent me from only exporting the type of Player without exporting the whole class as well.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated add typescript documentation videojs.com#179
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[welcome]

💖 Thanks for opening this pull request! 💖

Things that will help get your PR across the finish line:

• Run npm run lint -- --errors locally to catch formatting errors earlier.
• Include tests when adding/changing behavior.
• Include screenshots and animated GIFs whenever possible.

We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[uzbeki]

that looks like a decent addition to its types.