Add readlink -f flag to CocoaPods script to workaround Xcode 14.3 issue

[jmagman]

Xcode 14.3 (released March 30, 2023) changed the readlink symlink behavior to be relative from the script working directory, instead of the relative path of the symlink. A CocoaPods script generated as source="$(readlink "${source}")" but with the new behavior should be source="$(readlink -f "${source}")". CocoaPods updated their script at CocoaPods/CocoaPods#11828, but hasn't yet released it.

This caused a failure when archiving/flutter build ipaing iOS or macOS Flutter apps (build seems to succeed):

    Symlinked...
    rsync --delete -av --filter P .*.?????? --links --filter "- CVS/" --filter
    "- .svn/" --filter "- .git/" --filter "- .hg/" --filter "- Headers" --filter
    "- PrivateHeaders" --filter "- Modules"
    "../../../IntermediateBuildFilesPath/UninstalledProducts/iphoneos/url_launch
    er_ios.framework"
    "/Users/m/Library/Developer/Xcode/DerivedData/Runner-gnengnkipgqsumexkv
    wkdczgvrst/Build/Intermediates.noindex/ArchiveIntermediates/Runner/Installat
    ionBuildProductsLocation/Applications/Runner.app/Frameworks"
    building file list ... rsync: link_stat

Add a migrator to copy the CocoaPods workaround and update the generated CocoaPods script so that users don't need to update CocoaPods when they update to Xcode 14.3. Only run the migrator when Xcode >=14.3.

Confirmed on this PR:

• iOS apps can be archived successfully on Xcode 14.3
• macOS apps can be archived successfully on Xcode 14.3
• the migrator doesn't run on 14.2
• the migration only runs once on 14.3
• after run once, subsequent runs do not kick off a new pod install
• manually running pod install again after the migration does restore the old behavior, but running flutter build/run again will re-run the migrator.

Fixes #123890

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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[vashworth]

LGTM

[christopherfujino]

LGTM