CLI: union leafref not supported in completion

[olofhagsand]

The following construct is not supported for completion in the CLI:

          leaf myleaf  {
                type union {
                    type leafref {
                        path "<somewhere>";
                    }
                    type leafref {
                        path <somewhere else>";
                    }
                }

For example, when doing a completion operation in the CLI, no alternatives show up:

   cli> myleaf ?
   <string>

It is supported when validating and committing configurations though.