[FIX] MockServer: fix the OData system query selection
[FIX] MockServer: fix the OData system query selection

Nested selection queries lead to an issue (MODELS/INAMAPPING/ServiceURI)
since the old implementation handles them incorrect. Also this fixes the
assignment of the __metadata to any property.

Change-Id: I2b4dcb22cae517c9ab39e786601cb2d4fad227fa
BCP: 2280133414

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