* 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

Build number (part after +) is documented as optional, use entire app version if not present (#37036)

Move tools tests into a general.shard directory in preparation to changing how we shard tools tests (#36108)

This PR aims at several things:

1. Use pub_semver to check a version in pubspec.yaml meets the requirements specified in https://semver.org/.
2. Don't limit build-number/build-name as a fixed format. Instead, validate it according to the target(ios/android).
3. Make sure that build-number/build-name are always validated no matter it's specified by the `flutter command` or version in pubspec.yaml.

Fixes #27589