[INTERNAL] core/ElementMetadata: #getDesignTime deprecated
[INTERNAL] core/ElementMetadata: #getDesignTime deprecated

To get rid of synchronous requests we remove the getDesignTime API.
Consumers should switch to #loadDesignTime instead.
See: I53edbf263387b43e5d9f08c543bdbf0efbee9ec4

Change-Id: I24e120f192f8303249ccda08cef55f7b73fdf423

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