Remove DebugPrints and replace them with coded return value

SafeRenderer safety critical code has dependencies to C++ headers that give big problems with FlexeLint. However, the C++ headers are not deemed necessary and there are ways to get rid of them.

One of the problematic C++ header dependencies is related to debug prints. As the debug prints are difficult to export to host application anyway (and there is no obvious standard way), it was decided to remove the prints and replace them by coded return values. I.e. the process or supervisor starting the SafeRenderer gets possible error indications as return values from the SafeRenderer application.

The error messages have to be found and given error value instead. Preferably different modules have different error value ranges so some designing is needed as well as changing functions to return error values in chained fashion. I.e. if leaf function stumbles to error first, it should return error value to supervisor even if there are other failures resulting from the first one.

Error codes should be documented for easy reference.