[FIX] sap.m.Panel: Documentation improved
[FIX] sap.m.Panel: Documentation improved

BCP: 2070154349
Fixes https://github.com/SAP/openui5/issues/2847
Change-Id: I65ab0bd8836a637784c413dea2dca2b2efc39091

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