Run all flutter/flutter iOS devicelab tests using iOS 18 physical device

[vashworth]

Prerequisites

• Xcode 16 is available in CIPD
• Upgrade 1 arm64 and x86 macOS 14 devicelab bot in staging pool to iOS 18 #148963

Instructions to run via led

Update to latest depot_tools by running gclient:

To run manual led test on a Mac-14, iOS-18 staging bot:

1. led get-builder "luci.flutter.staging:Mac_ios flutter_gallery_ios__start_up" > properties.json
2. Replace "sdk_version": "15a240d" with new Xcode build version (case sensitive with CIPD version)
3. cat properties.json | led edit -d os=Mac-14 | led edit -d device_os=iOS-18 | led edit-recipes-bundle | led launch

❗ File issues for tests that fail and add links to the issues in #148966. This is important so we can track any fixes that need to be cherrypicked to beta/stable and so steps that are steps are not completed before issues are resolved.