Update script to support building Qt 5.15.x on Ventura and above

[jcfr]

Related notes:

• https://discourse.slicer.org/t/transition-of-macos-preview-build-from-host-10-13-high-sierra-to-13-ventura/28668
• slicer-macos-preview: Transition build from factory-south-macos to computron Slicer/DashboardScripts#53 (comment)

cc: @jamesobutler

[jamesobutler]

Newer OS may be able to build latest Qt 5.15.x releases with potentially any compatibility fixes.

In an effort to update to latest lgpl available Qt 5.15.x I created https://github.com/jamesobutler/qt-easy-build/tree/5.15.13 and was successful in building this on an Intel based mac running macOS Big Sur 11.7.10. The script could further be improved to apply the latest Qt Webengine (5.15.16-lts) which I did manually.