[FIX] sap.m.MessageBox: Screen reader improvements
[FIX] sap.m.MessageBox: Screen reader improvements

Change-Id: I41d23a8994ee4a81ad32faeaadd31d8dd7bd048e
Signed-off-by: Deyan Yanakiev <2614bfd3515c6c39ab25ed6159ddb09df1e2cc71@sap.com>

olirogers/openui5,nzamani/openui5,cschuff/openui5,SQCLabs/openui5,nzamani/openui5,SAP/openui5,cschuff/openui5,SAP/openui5,SAP/openui5,SQCLabs/openui5,SQCLabs/openui5,SAP/openui5,olirogers/openui5,cschuff/openui5,nzamani/openui5,olirogers/openui5