libstdc++: Add Doxygen docs for std::forward_like

Also add "@since C++11" to std::move, std::forward etc.

libstdc++-v3/ChangeLog:

	* include/bits/move.h (forward, move, move_if_noexcept, addressof):
	Add @since to Doxygen comments.
	(forward_like): Add Doxygen comment.