Use Xcode DocC tool for buiding Apple platform docs + add quick-start tutorial #28704
### Pull Request Readiness Checklist
- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
This PR resolves https://github.com/opencv/opencv/issues/28702 and https://github.com/opencv/opencv/issues/28703
Additionally it resolves build issues on Apple platforms by making build scripts run with Python 3
Giles Payne
