Prepare application source code (C++ programming language files) for Qt6
compatibility. Implement alternative code paths where the API has changed
compared to Qt5. This unbreaks Mac OSX 12 builds with homebrew.
This change is based on work that was submitted by Dominik Sliwa
<dominik@sliwa.io>.
This patch was generated using clang-tidy:
clang-tidy -checks="-*,google-readability-namespace-comments" -fix
Switch to the format used by clang-tidy to allow easy, automatic,
tool-based maintenance / checking of the comments.
This also found a few instances of comments that were out of sync.