deps: Upgrade Flutter; and handle migrations

[rajveermalviya]

deps: Upgrade Flutter to 3.27.0-1.0.pre.443

And update Flutter's supporting libraries to match.

---

deps: Update CocoaPods to 1.16.2

Changelog:
https://github.com/CocoaPods/CocoaPods/blob/master/CHANGELOG.md#1162-2024-10-31

Upstream changed the recommended CocoaPods version to 1.16.2 in:
flutter/flutter@dff1916

Without this change flutter run generates the following warnings:

Warning: CocoaPods recommended version 1.16.2 or greater not installed.
Pods handling may fail on some projects involving plugins.
To update CocoaPods, see https://guides.cocoapods.org/using/getting-started.html#updating-cocoapods

---

intl: Migrate off of synthetic package; check-in generated files

flutter tool deprecated the package:flutter_gen synthetic package:
https://flutter.dev/to/flutter-gen-deprecation

So, instead migrate to referencing source files directly.

Without this change, flutter run generates the following warning:

Synthetic package output (package:flutter_gen) is deprecated: https://flutter.dev/to/flutter-gen-deprecation. In a future release, synthetic-package will default to `false` and will later be removed entirely.

[chrisbobbe]

Great!

If I understand correctly, the "migrate off synthetic package" commit fixes an issue I run into pretty often, where flutter_gen gets removed from .dart_tool/package_config.json which causes analysis failures everywhere we use localization, and I have to fix by running flutter pub get.

We have a chunk of code in tools/check to work around that issue:

    # The `flutter pub run` disrupts `.dart_tool/package_config.json`,
    # removing `flutter_gen`, which causes analysis failures everywhere
    # that we use localization.  (And `dart run` has the same problem.)
    # Fix it back, with `flutter pub get`.
    # TODO(upstream): Find or file a bug for this `pub run` vs. `flutter_gen` issue.
    if [ -n "${opt_verbose}" ]; then
        flutter pub get \
        || return
    else
        flutter pub get \
            >/dev/null \
        || return
    fi

And IIUC we can just delete that code now. 🎉.

git grep flutter_gen also finds an instruction in docs/translation.md that should be updated.

[gnprice]

Neat! Glad to see this fixed.

In addition to the points Chris mentioned above, let's add this directory to .gitattributes so that git log -p and so on don't become noisy; see the handling there of other generated files.

[gnprice]

Merging the first two commits now, to have the Flutter upgrade in when I make a new beta release shortly.

@rajveermalviya please go ahead and send the last commit:
6a49502 intl: Migrate off of synthetic package; check-in generated files

as a follow-up PR, after handling the comments above. Thanks again!

[gnprice]

(This means we'll have that warning appear on flutter run for the moment:

Synthetic package output (package:flutter_gen) is deprecated:
https://flutter.dev/to/flutter-gen-deprecation. In a future release, synthetic-package will default
to `false` and will later be removed entirely.

but that's tolerable, and we'll take care of it soon.)

[rajveermalviya]

send the last commit … as a follow-up PR

@gnprice Sent #1058.