Run all flutter/engine macOS tests using Xcode 16 and iOS 18 simulator

[vashworth]

Prerequisites

• Xcode 16 is available in CIPD
• Upgrade 50% of chromium bots to macOS 14.5 #148891 (assuming Xcode 16 requires macOS 14.5)
  • If Xcode 16 requires a higher macOS version, bots will need to be upgraded to new required version before doing this

Instructions

Make a PR that changes the .ci.yaml to use the new Xcode build version and run exclusively on macOS 14. Note that not all tests run in presubmit, so you'll likely need to do some of them via led or edit the .ci.yaml to run the tests in presubmit.

https://github.com/flutter/engine/blob/main/.ci.yaml

$flutter/osx_sdk : >-
        {
-          "sdk_version": "15a240d"
+          "sdk_version": "[insert new CIPD case-sensitive Xcode build version]"
        }
        
- os: Mac-13|Mac-14
+ os: Mac-14

https://github.com/flutter/engine/blob/main/ci/builders/local_engine.json
https://github.com/flutter/engine/blob/main/ci/builders/mac_android_aot_engine.json
https://github.com/flutter/engine/blob/main/ci/builders/mac_host_engine.json
https://github.com/flutter/engine/blob/main/ci/builders/mac_ios_engine.json
https://github.com/flutter/engine/blob/main/ci/builders/mac_unopt_debug_no_rbe.json

$flutter/osx_sdk : >-
        {
-          "sdk_version": "15a240d"
+          "sdk_version": "[insert new CIPD case-sensitive Xcode build version]"
        }
        
- os=Mac-13|Mac-14
+ os=Mac-14

https://github.com/flutter/engine/blob/main/ci/builders/mac_unopt.json

$flutter/osx_sdk : >-
        {
          "runtime_versions": [
-               "ios-17-0_15a240d"
+               "ios-18-0_[insert new CIPD case-sensitive Xcode build version]"
          ],
-          "sdk_version": "15a240d"
+          "sdk_version": "[insert new CIPD case-sensitive Xcode build version]"
        }
        
- os=Mac-13|Mac-14
+ os=Mac-14

https://github.com/flutter/engine/blob/main/testing/scenario_app/run_ios_tests.sh

- readonly OS_RUNTIME=com.apple.CoreSimulator.SimRuntime.iOS-17-0
- readonly OS="17.0"
+ readonly OS_RUNTIME=com.apple.CoreSimulator.SimRuntime.iOS-18-0
+ readonly OS="18.0"

In addition, golden files will need to be updated. See flutter/engine#49833 as example

❗ File issues for tests that fail and add links to the issues in #148898. 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.