Ensure well-timed support of the new Apple platforms on CI/CD

The recent experience with the intake of the new Apple Silicon platforms has shown a need for additional actions and better coordination in what we do to start supporting new releases of Apple SDKs and OSs on regular basis.

This epic holds separate tasks which are required to ensure well-timed support of the new Apple platforms: XCode 14, MacOS 13 and iOS 16. Though there is no official communication from Apple yet, the history (https://xcodereleases.com) lets us assume that there will be a beta release of XCode 14 around June 2022 with a final release around Sept 2022.

This timing pattern is very unfortunate for Qt since it hits the feature freeze and the final release on almost exactly the same months of a Fall release of Qt, for example, https://wiki.qt.io/Qt_6.4_Release. We still should see what we can do on the Fall release since shifting it to the Spring Qt release would be far too late for users.

It still makes sense to start with 6.4 and start now to get prepared for betas of Xcode in the early Summer.

There would be the following phases:

• In-take of the beta SDK and creation of nightly unblocking builds
• Turning on the auto-tests for nightly builds and treat all failures as insignificant
• Stabilize auto-tests on nightly builds
• In-take of the SDK in the staging CI cycles and marking failures as significant

Due to the above timing, we will not be able to commit a full support of the new SDK and platform releases in a dot-zero release. The target would be to ensure the first three steps are done in the dot-zero release and complete the last step for the first bug-fix release.

Still, the target is also to enable interested users and Qt developers to access early builds based on beta SDK for testing and their own development. This would ensure, that we are well prepared to make a final step when the new platforms are officially released by Apple.

Another side of the related works would be to ensure a sufficient footprint of new releases being available on hardware or VMs for any developer who needs this. But this is another work which shall be complete in teams and probably not tracked here