* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

* Broadcasting popRoute and pushRoute methods via SystemChannels.navigation. These messages will be used in flutter_web to detect the route

* Broadcasting popRoute and pushRoute methods via SystemChannels.navigation. These messages will be used in flutter_web to detect the route

* Reverting all unrelated formatting changes.

* Adding unit tests. Adding more comments.

* Changing string method names with constant strings.

* Fixing a constant strings.

* Fixing analyzer error.

* Fixing more white space.

* Changing the method names. Adding comments to the SystemChannels

* Comment and code name fixes

* replacing the comment with reviewer suggestion.

* addinf systemchannels.navigation mock to test bindings

* Adding a new class for sending route change notrifications. The nottifications are only sent on web. This should fix breaking android/ios

* using new class RouteNotificationMessages in navigator

* Fixing analyzer issues.

* fixing cycle dependency

* fixing github analyze error

* dartfmt two new classes. trying to fix anayze errors

* Update route_notification_messages.dart

* trying to fix white space errors