Handle duplicated values in sketching. (#6178)

* Accumulate weights in duplicated values.
* Fix device id in iterative dmatrix.

src/common/quantile.cuh

@@ -106,6 +106,8 @@ class SketchContainer {
   }
   /* \brief Return GPU ID for this container. */
   int32_t DeviceIdx() const { return device_; }
+  /* \brief Accumulate weights of duplicated entries in input. */
+  size_t ScanInput(Span<SketchEntry> entries, Span<OffsetT> d_columns_ptr_in);
   /* \brief Removes all the duplicated elements in quantile structure. */
   size_t Unique();
   /* Fix rounding error and re-establish invariance.  The error is mostly generated by the
@@ -121,7 +123,7 @@ class SketchContainer {
    * \param weights (optional) data weights.
    */
   void Push(Span<Entry const> entries, Span<size_t> columns_ptr,
-            common::Span<OffsetT const> cuts_ptr, size_t total_cuts,
+            common::Span<OffsetT> cuts_ptr, size_t total_cuts,
             Span<float> weights = {});
   /* \brief Prune the quantile structure.
    *