[libcxx][modularisation] moves <utility> content out of <type_traits>

Moves:

* `std::move`, `std::forward`, `std::declval`, and `std::swap` into
  `__utility/${FUNCTION_NAME}`.
* `std::swap_ranges` and `std::iter_swap` into
  `__algorithm/${FUNCTION_NAME}`

Differential Revision: https://reviews.llvm.org/D103734

NOKEYCHECK=True
GitOrigin-RevId: 6adbc83ee9e46b476e0f75d5671c3a21f675a936
diff --git a/include/variant b/include/variant
index 5a431c3..2145700 100644
--- a/include/variant
+++ b/include/variant
@@ -201,6 +201,7 @@
 
 #include <__availability>
 #include <__config>
+#include <__utility/forward.h>
 #include <__tuple>
 #include <array>
 #include <compare>