Feature/nullsafety (#372)
* Fixed fullscreenByDefault issue
* Updated documentation
* Updated documentation
* Refactored internal event handling.
* Refactored internal event handling.
* Added tests
* Added tests
* Tests refactor
* Null safety migration
* Fixed issue where player controls were immediately hidden.
* General refactor
* General refactor
* General refactor
* General refactor
* General refactor
* Null safety refactor
* Null safety refactor
* Null safety refactor
* Fixed initialized listener
* Removed cancelFullScreenDismiss parameter
* General refactor
* Added initialization check for VideoPlayerController
* Added initialization check for VideoPlayerController
* General refactor
* Changed default value of enableProgressText to true in BetterPlayerControlsConfiguration
* Setup first selected HLS Audio as default one.
* Lint & format update
* Updated changelog, lint fixes
* Commented analysis_options.yaml
