Allow configuring the flutter_manifest to support a synthetic package, this is done through flutter: generate: true.

When running pub get, insert a flutter_gen entry into the packages if it does not already exist. This points to .dart_tool/flutter_gen, which can be updated to contain the generated intl sources (But doesn't currently)

Adds an integration test that verifies this code can be run and imported when enabled.

Part of #60914

* Reland: [flutter_tool] Where possible, catch only subtypes of Exception

* Add armv7f to getIOSArchForName

This reverts commit 57c6721c.

This reverts commit 9de7787f.

This reverts commit f1cd47ef.

This reverts commit 0a38f29c.

* 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/lib

* address review comments

* use castStringKeyedMap

* introduce {bool,string,strings}Arg

* fix ci

This reverts commit 3597bae6.

When we were running `pub` within `flutter pub`, we were
unconditionally including the `--verbosity=warning` argument.
Then we were conditionally including `--verbose` if we were
running in verbose mode.  However, the former argument
supersedes the latter, and we were never able to run `pub`
in verbose mode.

* more ui-as-code

* address review comments