Revert "flutter_tools: Remove unused //ignore comments; change flutter-specific ones to "ignore_for_flutter" (#45917)" (#46999)

This reverts commit f2859201.

It broke forbidden_imports_test, which uses a custom ignore directive.

flutter_tools: Remove unused //ignore comments; change flutter-specific ones to "ignore_for_flutter" (#45917)

* 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

* implicit-casts:false on flutter_tools

* use castStringKeyedMap

* address review comments

* address review comments

* fix issues after rebase

An optimization to the coverage collection speed was added in #30811. This commit further expands on it to parameterize the CoverageCollector with a custom predicate, allowing internal use cases to filter the RPC calls to the Dart VM based on scripts of interest to coverage collection.

Extracted from https://github.com/flutter/flutter/pull/36205