1. We were not always able to clean up `resize` on the `ResizeManager`, as the iframe
contentWindow can disappear before dispose
2. Native Tracks on Safari do not have an `off` so we have to deal with
event listeners manually
Fixes#5878
- Get rid of our custom XHR shim. Export it as videojs.xhr.
- Updated XHR to be stubbed everywhere in tests to prevent errors.
- Added npm install to the review process
closes#2318closes#2594
- Fixed a console error in dom tests from loading a track source
- Switched to non-fetching poster urls in tests to prevent errors
- Stubbed XHR for TextTrack tests to prevent log errors
- Fixed text track console errors that stubbing async didn't catch
because there's some async happening in tracks that makes it so
- XHR isn't even used until the test is complete
- Removed extra code
- Added player.dispose more places and fixed attributes test
