Use cuda::stream_ref::sync() for the table-init stream sync (review: bdice)

Replace the CUDF_CUDA_TRY(cudaStreamSynchronize(stream.get())) calls added for
stream safety with the idiomatic stream.sync() in all three find_or_initialize
lambdas.

Author: brandon-b-miller

cpp/src/strings/utilities.cu

@@ -110,7 +110,7 @@ character_flags_table_type const* get_character_flags_table(cuda::stream_ref str
     // The copy above is asynchronous and the cached pointer is shared across
     // callers/streams; synchronize so the table is fully populated before it is
     // handed out (first-use only).
-    CUDF_CUDA_TRY(cudaStreamSynchronize(stream.get()));
+    stream.sync();
     return table;
   });
 }
@@ -132,7 +132,7 @@ character_cases_table_type const* get_character_cases_table(cuda::stream_ref str
     // The copy above is asynchronous and the cached pointer is shared across
     // callers/streams; synchronize so the table is fully populated before it is
     // handed out (first-use only).
-    CUDF_CUDA_TRY(cudaStreamSynchronize(stream.get()));
+    stream.sync();
     return table;
   });
 }
@@ -154,7 +154,7 @@ special_case_mapping const* get_special_case_mapping_table(cuda::stream_ref stre
     // The copy above is asynchronous and the cached pointer is shared across
     // callers/streams; synchronize so the table is fully populated before it is
     // handed out (first-use only).
-    CUDF_CUDA_TRY(cudaStreamSynchronize(stream.get()));
+    stream.sync();
     return table;
   });
 }