Update examples to use metal as default graphics API on mac

[iche033]

🦟 Bug fix

#914

Summary

Use metal as default graphics API on macOs

A couple of other minor fixes:

• Fix simple_demo_qml deprecation warnings
• stop loading optix engine as one of the default engines

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #937 (c91ace5) into gz-rendering7 (adb0f1c) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

❗ Current head c91ace5 differs from pull request most recent head 522e36c. Consider uploading reports for the commit 522e36c to get more accurate results

@@                Coverage Diff                @@
##           gz-rendering7     #937      +/-   ##
=================================================
- Coverage          77.63%   77.62%   -0.02%     
=================================================
  Files                170      170              
  Lines              14724    14726       +2     
=================================================
  Hits               11431    11431              
- Misses              3293     3295       +2     

Files	Coverage Δ
src/Utils.cc	62.68% <0.00%> (-0.95%)	⬇️