DDSXTY14 — Enums with different holder types should not be assignable

The row for ENUM_TYPE in Table 40 defines an enum's holder type.

Footnote 3 on page 63 indicates that the type system is designed to allow a DataReader to consume a byte stream from a differently-typed (but assignable) DataWriter without "requiring the consultation of per-DataWriter type definitions during sample deserialization".

The current definition of Enum Assignability fails in this respect. It needs to prevent enum types from being assignable when their holder types differ.

Also relevant - pgh 2 of 7.2.4.2 "...Enumerated types (Enumeration and Bitmask) are delimited types as their serialized size is fixed"