[libc++][pstl] Merge all frontend functions for the PSTL (#89219)

This is an intermediate step towards the PSTL dispatching mechanism
rework. It will make it a lot easier to track the upcoming front-end
changes. After the rework, there are basically no implementation details
in the front-end, so the definition of each algorithm will become much
simpler. Otherwise, it wouldn't make sense to define all the algorithms
in the same header.
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 869fc19..a522a60 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -1882,22 +1882,7 @@
 #if _LIBCPP_STD_VER >= 17
 #  include <__algorithm/clamp.h>
 #  include <__algorithm/for_each_n.h>
-#  include <__algorithm/pstl_any_all_none_of.h>
-#  include <__algorithm/pstl_copy.h>
-#  include <__algorithm/pstl_count.h>
-#  include <__algorithm/pstl_equal.h>
-#  include <__algorithm/pstl_fill.h>
-#  include <__algorithm/pstl_find.h>
-#  include <__algorithm/pstl_for_each.h>
-#  include <__algorithm/pstl_generate.h>
-#  include <__algorithm/pstl_is_partitioned.h>
-#  include <__algorithm/pstl_merge.h>
-#  include <__algorithm/pstl_move.h>
-#  include <__algorithm/pstl_replace.h>
-#  include <__algorithm/pstl_rotate_copy.h>
-#  include <__algorithm/pstl_sort.h>
-#  include <__algorithm/pstl_stable_sort.h>
-#  include <__algorithm/pstl_transform.h>
+#  include <__algorithm/pstl.h>
 #  include <__algorithm/sample.h>
 #endif // _LIBCPP_STD_VER >= 17