[url_launcher] Add Swift Package Manager integration to example app

[loic-sharma]

This migrates the example app to have Swift Package Manager integration. This raises the example app's Flutter SDK requirement to 3.24.0 or higher.

Scenarios:

1. Run the example app using Flutter 3.24 or higher with SwiftPM feature on: Plugin is added using Swift Package Manager.
2. Run the example app using Flutter 3.24 or higher with SwiftPM feature off: Plugin is added using CocoaPods. The tool generates an empty FlutterGeneratedPluginSwiftPackage local package.
3. Run the example app using Flutter version lower than 3.24: you get a build error because the example app's Xcode project expects a FlutterGeneratedPluginSwiftPackage local package but cannot find it.

Part of: flutter/flutter#159173

Tests

Current tests build the example apps twice: once with SwiftPM on, once with SwiftPM off.

Currently, the tests with SwiftPM on also migrate the example app to add SwiftPM integration. After this change, these tests will no longer need to migrate the example app as it is already migrated.

In other words, this change is covered by existing tests.

Migration steps

The app was migrated using these steps:

flutter channel master
flutter upgrade
flutter config --enable-swift-package-manager
flutter build ios --config-only
flutter build macos --config-only

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or this PR is exempt from CHANGELOG changes.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption, contact "@test-exemption-reviewer" in the #hackers channel in Discord (don't just cc them here, they won't see it!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing. The test exemption team is a small volunteer group, so all reviewers should feel empowered to ask for tests, without delegating that responsibility entirely to the test exemption group.

[stuartmorgan]

test-exempt: configuration change

[stuartmorgan]

LGTM

[auto-submit]

A reason for requesting a revert of flutter/packages/8128 could
not be found or the reason was not properly formatted. Begin a comment with 'Reason for revert:' to tell the bot why
this issue is being reverted.

[loic-sharma]

Reason for revert: this caused the license checker to error:

The license block for these files is missing or incorrect:
  /b/s/w/ir/x/w/packages/packages/url_launcher/url_launcher/example/ios/Flutter/ephemeral/Packages/FlutterGeneratedPluginSwiftPackage/Package.swift
  /b/s/w/ir/x/w/packages/packages/url_launcher/url_launcher/example/ios/Flutter/ephemeral/Packages/FlutterGeneratedPluginSwiftPackage/Sources/FlutterGeneratedPluginSwiftPackage/FlutterGeneratedPluginSwiftPackage.swift
  /b/s/w/ir/x/w/packages/packages/url_launcher/url_launcher/example/macos/Flutter/ephemeral/Packages/FlutterGeneratedPluginSwiftPackage/Package.swift
  /b/s/w/ir/x/w/packages/packages/url_launcher/url_launcher/example/macos/Flutter/ephemeral/Packages/FlutterGeneratedPluginSwiftPackage/Sources/FlutterGeneratedPluginSwiftPackage/FlutterGeneratedPluginSwiftPackage.swift
If this third-party code, move it to a "third_party/" directory, otherwise ensure that you are using the exact copyright and license text used by all first-party files in this repository.