CPP1116 — Annotation for union discriminator name

For the switch of unions, the C++ mapping uses the name _d.
It would be desirable to permit names that reflect the users' application domain.
Example:

  enum environment_t { air, water, land };

  union env_info_t switch (@switchname("environment") environment_t) {
    case air:
      air_info_t air_info;
    case water:
       [...]
  };

The @switchname annotation would cause a getter/setter of the given name to be generated in addition to the _d() accessors.
In the above example:

  void environment(environment_t);  // alias for _d(environment_t)
  environment_t environment() const;  // alias for _d()

Depends on an IDL spec change

Defer until the IDL 4.3 RTF resolves IDL43-42.