Update flutter/packages to use Xcode 26, iOS 26 Simulator, and macOS 15 #172859
Description
Prerequisites
- Run all flutter/packages macOS tests using Xcode 26 and iOS 26 simulator #172856
- Upgrade remaining chromium bots in each pool to macOS 15.5 #167841
- Ensure no open issues in ☂️ Tracking issue for any infra or test failures with Xcode 26 and iOS 26 Simulators #172857 under flutter/packages
Instructions
TODO