Improve print formatting of strings containing newline characters. (N…

…VIDIA#11108)

String data that contained \r and \n characters would print badly mangled.  

Example column containing:
```
.,e,Infinity,+Infinity,-Infinity,+nAn,-naN,Nan,5f,1.2f,\riNf,NULL
```

Doing a `cudf::test::print()` on this would yield mostly garbage, but importantly, plausible-seeming but puzzling garbage:

```
iNf,NULLnity,+Infinity,-Infinity,+nAn,-naN,Nan,5f,1.2f,
```

The fix is to do a little postprocessing and replace the individual chars `'\r'` and `'\n'` with the escaped strings `"\r"` and `"\n"`.  Note that this only applies to the output ultimately sent to the print - not to the raw data retrieved from the device itself using `::to_host`

Authors:
  - https://github.com/nvdbaranec

Approvers:
  - David Wendt (https://github.com/davidwendt)
  - Mike Wilson (https://github.com/hyperbolic2346)
  - Bradley Dice (https://github.com/bdice)
  - Karthikeyan (https://github.com/karthikeyann)

URL: rapidsai/cudf#11108

cpp/tests/utilities/column_utilities.cu

@@ -1054,13 +1054,26 @@ struct column_view_printer {
     if (col.is_empty()) return;
     auto h_data = cudf::test::to_host<std::string>(col);
 
+    // explicitly replace '\r' and '\n' characters with "\r" and "\n" strings respectively.
+    auto cleaned = [](std::string_view in) {
+      std::string out(in);
+      auto replace_char = [](std::string& out, char c, std::string_view repl) {
+        for (std::string::size_type pos{}; out.npos != (pos = out.find(c, pos)); pos++) {
+          out.replace(pos, 1, repl);
+        }
+      };
+      replace_char(out, '\r', "\\r");
+      replace_char(out, '\n', "\\n");
+      return out;
+    };
+
     out.resize(col.size());
     std::transform(thrust::make_counting_iterator(size_type{0}),
                    thrust::make_counting_iterator(col.size()),
                    out.begin(),
-                   [&h_data](auto idx) {
+                   [&](auto idx) {
                      return h_data.second.empty() || bit_is_set(h_data.second.data(), idx)
-                              ? h_data.first[idx]
+                              ? cleaned(h_data.first[idx])
                               : std::string("NULL");
                    });
   }