ENH: improve demangled symbol names for safePrintStack

- parse out symbols and use abi::__cxa_demangle for more readable
  names in safePrintStack.

- shorten prefixed /path/openfoam/platforms/lib/... to start
  with "platforms/lib/..." to avoid unreadably long lines.

- improved file-scope localization of helper functions.

STYLE: use std::ios_base::basefield instead of dec|oct|hex for masking