Convert Function Metamodel to built-in relational model MED

In order to retire the Function metamodel we need to replace it with extension properties on the relational metamodel via the new MED framework.

in 7.5/7.6 the "Source Function" property (deterministic) is the only current built-in "relational" extended property.

Probably could convert to use only 1 built-in MED that extends "Relational" metamodel.