Fix Qt < 5.3 compat. issue in DebugOutput;
AppDebugMessageHandler: Filter out verbose QPainter warnings on Linux Qt < 5.3; Do not return any instance if disabled entirely;
Fix style sheet for simulator radio background.
* [Companion][Simulator] Add custom qDebug message handler/formatter as an option. Keeps support for QT_MESSAGE_PATTERN env. var.
* [Simulator] Show system messages of level qInfo and above in debug console.
* [Simulator] Still capture screenshot to clipboard if path is not accessible (and screenshot results now print to simulator debug console).
* Fix for older CMake.
* [Companion] Do not start debug message handler if app is shutting down, and add null checks before using it; Increase backtrace report depth; Add OTx headers; Add Companion exit status debug; Clean up unused code.
* [Simulator] Add asynchronous FIFO buffer for handling debug output/display more efficiently. (#4488)
(cherry-picked from b12bd7d7be)
Max Paperno