Define inheritance for enumeration types

Proposed Proposal Allow EnumType to specify a BaseType to which the EnumType will add new members. BaseType and UnderlyingType cannot be both specified, the UnderlyingType. In metadata annotations the EnumMember syntax requires prefixing the member name with the fully qualified type name in all cases, so there's no ambiguity if the same base enum type is extended by more than one other enum type. For properties and instance annotations in request and response bodies enum members are represented only as the member name without the type name prefix if the member is defined by the declared type of the property. Members of a derived type must be prefixed with the qualified type name. This is consistent with the metadata annotation syntax and the URL syntax for accessing properties of derived types: "PrimaryColor":"Yellow" "SecondaryColor":"org.example.ExtendedPattern/DarkRed"