fix Issue 10096 - __traits(allMembers) triggers out of bounds error

Internal member names should not be listed in __traits(allMembers)
- Names starting double underscore does not appear its result.
  __cpctor, __invariant, __xopEquals, __fieldPostBlit,
  __aggrPostBlit, __fieldDtor, __aggrDtor, and others...
- Except __ctor, __dtor, and __postblit. They are already used in Phobos, so
  temporary keep them for backward compatibility.