Reland #97243 reverted in #97614.

Instead of making the IPA a tool failure, instead log the error but exit successfully since the step 1 below still succeeded.

flutter build ipa has two stages for iOS distribution:

1. Archive the app into an xcarchive bundle.
2. Optionally, export the xcarchive into an ipa bundle for distribution to the App Store, or to a device, or enterprise distribution...

Currently to get to number 2 and create the ipa file users need to pass in a --export-options-plist file, which they need to create themselves, or know how to yank off a previously-build IPA. Flutter's iOS distribution docs don't say what needs to go into the plist, it just points to Apple docs, or tells them to launch Xcode and create the IPA there.

1. Run flutter build ipa to produce a build archive.

Note: When you export your app at the end of Distribute App, Xcode will create a directory containing an IPA of your app and an ExportOptions.plist file. You can create new IPAs with the same options without launching Xcode by running flutter build ipa --export-options-plist=path/to/ExportOptions.plist. See xcodebuild -h for details about the keys in this property list.

2. Open build/ios/archive/MyApp.xcarchive in Xcode.

In this PR, if the user doesn't pass --export-options-plist, instead of bailing after the xcarchive, assume the user wants the most common case: to distribute their app to the App Store via the new --export-method option and its default app-store. Create the plist if one isn't passed in, with reasonable defaults for the most common settings for a Flutter app. If it fails (they haven't registered their app bundle ID for example), suggest they open the archive in Xcode and go through its wizard, as the docs currently suggest.

Allow the user to also specify --export-method ad-hoc or --export-method development or --export-method enterprise. See https://developer.apple.com/forums/thread/100614 for the distinction.

If the user has a more complicated scenario, they can continue to create their own plist via --export-options-plist, or open with Xcode.

We can add other options in the future for other values in the generated plist, if developers request it.

Command logging examples

Success

$ flutter build ipa
Running "flutter pub get" in veggieseasons...                    1,814ms
Archiving dev.flutter.VeggieSeasons...
Automatically signing iOS for device deployment using specified development team in Xcode project: S8QB4VV633
Running Xcode build...
 └─Compiling, linking and signing...                        12.3s
Xcode archive done.                                         38.6s
Built /Users/m/Projects/samples/veggieseasons/build/ios/archive/Runner.xcarchive.

💪 Building with sound null safety 💪

Building App Store IPA...                                          32.3s
Built IPA to /Users/m/Projects/samples/veggieseasons/build/ios/ipa.
To upload to the App Store either:
    1. Drag and drop the "build/ios/ipa/*.ipa" bundle into the Apple Transport macOS app https://apps.apple.com/us/app/transporter/id1450874784
    2. Run "xcrun altool --upload-app --type ios -f build/ios/ipa/*.ipa --apiKey your_api_key --apiIssuer your_issuer_id".
       See "man altool" for details about how to authenticate with the App Store Connect API key.

Flag validation error

$ flutter build ipa --export-options-plist foo.plist --export-method ad-hoc
"--export-options-plist" is not compatible with "--export-method". Either use "--export-options-plist" and a plist describing how the IPA should be exported by Xcode, or use "--export-method" to create a new plist.
See "xcodebuild -h" for available exportOptionsPlist keys.

IPA creation failure

The bundle identifier isn't set up, which needs to be resolved in Xcode's UI:

$ flutter build ipa --export-method ad-hoc
...
Built /Users/m/Projects/test_create/build/ios/archive/Runner.xcarchive.
...
Building ad-hoc IPA...                                           2,123ms
Encountered error while creating the IPA:
error: exportArchive: Failed to register bundle identifier
error: exportArchive: No profiles for 'com.example.testCreate' were found


Try distributing the app in Xcode: "open /Users/m/Projects/test_create/build/ios/archive/Runner.xcarchive"

Help text

    --export-method                                 Specify how the IPA will be distributed.

          [ad-hoc]                                  Distribute to designated devices that do not need to be registered with the Apple developer account. Requires a distribution certificate.
          [app-store] (default)                     Upload to the App Store.
          [development]                             Distribute only to development devices registered with the Apple developer account.

Fixes #97179

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• 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.

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