Deprecate KConcatenateRowsProxyModel also by compiler & runtime warnings
With Qt 5.13 now the min. required Qt version, everyone should be now encouraged to port away to QConcatenateTablesProxyModel
For the runtime warning with the QML type, the idea to use a separate logging category came up during discussion of kdeclarative!36 (closed) Would be curious if there is a standard approach to that we should/could use here instead.