[INTERNAL][FIX] sap.m.PlanningCalendar: Documentation fix
[INTERNAL][FIX] sap.m.PlanningCalendar: Documentation fix

In order to be visible in the documentation, "public" tag is added
to the doc of the setCustomAppointmentsSorterCallback method.

Change-Id: Iee155f8314070080ea0aa2f7add87134176a7d7e

SAP/openui5,cschuff/openui5,SAP/openui5,SAP/openui5,SAP/openui5,cschuff/openui5,cschuff/openui5