Add missing includes for cuda::std::abs (rapidsai#21845)

Followup of rapidsai#21703

This PR addresses rapidsai#21703 (comment) to add missing includes for `cuda::std::abs`.

Authors:
  - Yunsong Wang (https://github.com/PointKernel)

Approvers:
  - Bradley Dice (https://github.com/bdice)
  - Shruti Shivakumar (https://github.com/shrshi)
  - Nghia Truong (https://github.com/ttnghia)
  - Muhammad Haseeb (https://github.com/mhaseeb123)

URL: rapidsai#21845

Author: PointKernel

cpp/include/cudf/strings/detail/convert/string_to_float.cuh

@@ -8,10 +8,9 @@
 #include <cudf/strings/detail/convert/is_float.cuh>
 #include <cudf/strings/string_view.cuh>
 
+#include <cuda/std/cmath>
 #include <cuda/std/limits>
 
-#include <cmath>
-
 namespace cudf {
 namespace strings {
 namespace detail {

cpp/src/quantiles/tdigest/tdigest.cu

@@ -24,6 +24,7 @@
 
 #include <cuda/functional>
 #include <cuda/iterator>
+#include <cuda/std/cmath>
 #include <cuda/std/utility>
 #include <thrust/binary_search.h>
 #include <thrust/execution_policy.h>