ECMGenerateExportHeader: add macros for enumerator deprecation warning
With more consumers of KDE Frameworks already moving to using C++17 and not just waiting for that for Qt6, it would be good to also start making use of the enumeration deprecation attributes available with those C++ standards, to apply the compiler as messenger about usage of deprecated enum values and not just rely on the "surprise, it's gone" package via the API visibility controls.
See usage example:
Edited by Friedrich W. H. Kossebau