Fixes https://github.com/flutter/flutter/issues/134566.
Prior to this fix, `ShutdownHooks` were run in the private helper
function `_exit()` defined in the `package:flutter_tools/runner.dart`
library. Independent of this, the tool had signal handling logic that
traps SIGINT and SIGTERM. However, these handlers called `exit()` from
`dart:io`, and didn't run these hooks.
This PR moves the `_exit()` private helper to
`package:flutter_tools/src/base/process.dart` and renames it to
`exitWithHooks()`, so that it can be called by the signal handlers in
`package:flutter_tools/src/base/signals.dart`.
* 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
