[Closed Captioning] Create SubRip file parser and dart closed caption data object

[johnsonmh]

Description

This PR specifies a dart object that represents a "Closed Caption". This will be useful in a follow up PR, where I will add closed caption support the the VideoPlayerController.

Related Issues

flutter/flutter#25388

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[rami-a]

LGTM

[mklim]

Thank you for the contribution! The approach is good, but there's a few things that I think should be changed before landing.

[mklim]

nit: Some test cases for what happens with invalid input would be great, too.

[johnsonmh]

Done

[mklim]

The unit test is failing in CI, but it's not obvious to me why:

00:07 +12 -1: /tmp/cirrus-ci-build/packages/video_player/video_player/test/sub_rip_file_test.dart: Parses SubRip file [E]                                                                              
  Unsupported operation: _Namespace
  package:dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 196:49      throw_
  package:dart-sdk/lib/_internal/js_dev_runtime/patch/io_patch.dart 202:5                   get _namespace
  package:dart-sdk/lib/io/file_impl.dart 488:31                                             openSync
  package:dart-sdk/lib/io/file_impl.dart 549:18                                             readAsBytesSync
  package:dart-sdk/lib/io/file_impl.dart 594:18                                             readAsStringSync
  sub_rip_file_test.dart 15:31                                                              <fn>
  package:test_api                                                                          <fn>

Just double checking, it passes locally? the js_dev_runtime part looks suspicious to me, maybe this has something to do with the federated web implementation?

video_player's minor version should be bumped in pubspec.yaml and CHANGELOG.md now since it's been moved into that package.

Other than that the implementation here looks solid.

[mklim]

LGTM, thanks for the fix!