Adds iOS platform support to the unified build script, enabling
building of test-apps/daily-notification-test for iOS alongside
existing Android support.
Changes:
- Add build_plugin_for_test_app_ios() to build iOS test app
- Add build_ios() function for iOS platform handling
- Make environment checks conditional based on target platform
- Add get_pod_command() helper to handle CocoaPods via rbenv
- Update main() to accept --platform ios and include iOS in "all"
This aligns the script with BUILDING.md documentation (lines 71, 75)
which implied iOS support was already available. The iOS build
process mirrors Android: creates plugin symlink, builds Vue app,
syncs Capacitor iOS (handles Podfile fixes), and builds with
xcodebuild for simulator.
Platform-specific environment checks allow iOS-only builds without
requiring Android toolchain, and vice versa.