[libc++] Fix the handling of `views::take` for `iota_view` (#75683)

Currently, when libc++'s views::take specially handles an iota_view, the
addition is done after dereferencing the beginning iterator. However, in
[range.take.overview]/2.3, the addition is done before the dereferencing,
which means that the standard requires the returned iota_view to have
the same W and Bound type in such cases.

This patch fixes that, and also fixes a test that was testing the 
incorrect behavior.

Fixes #75611