Update to OpenXR 1.0.20

[cmbruns]

• On Linux:
  • [x] Update and install latest OpenXR-SDK from github
  • [x] Update latest OpenXR-Registry from github
  • [x] Build and install libclang
  • [x] Pull latest pyopenxr sources from github
  • [x] Generate: Run CMake and configure src/generate/CMakeLists.txt with build folder outside of src.
  • [x] Run tests
  • [x] Commit to local repository
  • [x] Push to github
• On Windows:
  • [x] Update and install latest OpenXR-SDK from github
  • [x] On Windows, be sure to set the DYNAMIC_LOADER option in CMake, because we need a shared DLL library.
  • [x] Update latest OpenXR-Registry from github
  • [x] Build and install libclang
  • [x] Pull latest pyopenxr sources from github
  • [x] Generate: Run CMake and configure src/generate/CMakeLists.txt with build folder outside of src.
  • [x] Run tests
  • [x] Commit to local repository
  • [x] python -m build --sdist --wheel
  • [x] twine upload --repository pypi dist/*
  • [x] Create tag like 1.0.1901 at current HEAD
  • [x] Push to github INCLUDING TAGS
  • [x] Write release notes and publish release on github