[libc++][ranges][NFC] Mark ranges::slide_view in progress (#68056)

Mark `ranges::slide_view` implementation as in progress.

Author: hawkinsw

libcxx/docs/Status/RangesViews.csv

@@ -29,7 +29,7 @@ C++23,`zip_transform <https://wg21.link/P2321R2>`_,Hui Xie,No patch yet,Not star
 C++23,`adjacent <https://wg21.link/P2321R2>`_,Hui Xie,No patch yet,Not started
 C++23,`adjacent_transform <https://wg21.link/P2321R2>`_,Hui Xie,No patch yet,Not started
 C++23,`join_with <https://wg21.link/P2441R2>`_,Unassigned,No patch yet,Not started
-C++23,`slide <https://wg21.link/P2442R1>`_,Unassigned,No patch yet,Not started
+C++23,`slide <https://wg21.link/P2442R1>`_,Will Hawkins,`67146 <https://github.com/llvm/llvm-project/pull/67146>`_,In Progress
 C++23,`chunk <https://wg21.link/P2442R1>`_,Unassigned,No patch yet,Not started
 C++23,`chunk_by <https://wg21.link/P2443R1>`_,Jakub Mazurkiewicz,`D144767 <https://llvm.org/D144767>`_,✅
 C++23,`as_const <https://wg21.link/P2278R4>`_,Unassigned,No patch yet,Not started