gitlab-ci: Add macos-arm64 jobs for Ninja and Xcode

For now, leave these jobs out during merge requests.

Rename existing macos-* build and test jobs to macos-x86_64-*, and add macos-arm64-* jobs.

Use our Qt macOS 10.13+ package for all macOS jobs since it provides Qt as a universal binary for x86_64 and arm64.

Backport: release