0.28.0-dev.0

https://pub.dev/packages/rxdart/versions/0.28.0-dev.0

Feedback on this change appreciated as this is a dev release before 0.28.0 stable!

ValueStream:
- Add lastEventOrNull getter to ValueStream, which returns the last emitted event (either data/value or error event), or null.
- Add isLastEventValue, isLastEventError and errorAndStackTraceOrNull extension getters to ValueStream, to check the kind of the last emitted event is data/value or error.
- Update documentation.
ReplayStream:
- Add errorAndStackTraces to ReplayStream, which returns a list of emitted ErrorAndStackTraces.
Rename Notification and Kind to better reflect their purpose, and to avoid confusion with Flutter's Notification class.
- Rename Notification to StreamNotification
  - Notification.onData to StreamNotification.data.
  - Notification.onDone to StreamNotification.done.
  - Notification.onError to StreamNotification.error.
- Rename Kind to NotificationKind
  - Kind.onData to NotificationKind.data.
  - Kind.onError to NotificationKind.error.
  - Kind.onDone to NotificationKind.done.
- Introduce DataNotification, ErrorNotification and DoneNotification as the subclasses of StreamNotification.
- Convert isOnData, isOnError, isOnDone, requireData to extension getters on StreamNotification, they are now named isData, isError, isDone and requireDataValue.
- Add extensions on StreamNotification: dataValueOrNull, requireErrorAndStackTrace, errorAndStackTraceOrNull getters and when method.

docs(using): fix typo by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/704
improve Notification.toString(), add tests for Notifications by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/703
fix example on README by @wurikiji in https://github.com/ReactiveX/rxdart/pull/712
Create .github/dependabot.yml by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/714
update example github_search by @hoangchungk53qx1 in https://github.com/ReactiveX/rxdart/pull/717
Fix lints and accept Dart SDK versions above 3.0 by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/721
feat(ValueStream): add lastEventOrNull, isLastEventValue, isLastEventError, errorAndStackTraceOrNull by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/729
refactor(utils): rename Notification to StreamNotification, Kind to NotificationKind by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/731
docs: update docs by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/733
chore(publish): prepare for v0.28.0-dev.0 by @hoc081098 in https://github.com/ReactiveX/rxdart/pull/734

@wurikiji made their first contribution in https://github.com/ReactiveX/rxdart/pull/712
@hoangchungk53qx1 made their first contribution in https://github.com/ReactiveX/rxdart/pull/717

Full Changelog: https://github.com/ReactiveX/rxdart/compare/0.27.7...0.28.0-dev.0