P2164R9 views::enumerate

Editorial changes:
* Added missing "views::" qualification in example
* Added missing "friend" in itemdecls
* Fixed "pos_" to "i.pos_" in iter_move definition
* Removed erroneous and unused default argument "pos = 0"

Fixes NB FR 021, US 108 (C++23 CD).

Author: burblebee