Use unicode strings in data generation by default (#132028)

In #132018, we found an issue with non-ascii strings in ignored source. 
This issue was not exposed by the data generation tests because these tests
use ascii-only strings. This patch updates the tests to instead use full
unicode strings by default.

Author: jordan-powers

test/framework/src/main/java/org/elasticsearch/datageneration/datasource/DefaultObjectGenerationHandler.java

@@ -15,9 +15,9 @@
 import java.util.Optional;
 import java.util.Set;
 
-import static org.elasticsearch.test.ESTestCase.randomAlphaOfLengthBetween;
 import static org.elasticsearch.test.ESTestCase.randomDouble;
 import static org.elasticsearch.test.ESTestCase.randomIntBetween;
+import static org.elasticsearch.test.ESTestCase.randomRealisticUnicodeOfCodepointLengthBetween;
 
 public class DefaultObjectGenerationHandler implements DataSourceHandler {
     @Override
@@ -49,7 +49,17 @@ public boolean generateRegularSubObject() {
 
             @Override
             public String generateFieldName() {
-                return randomAlphaOfLengthBetween(1, 10);
+                while (true) {
+                    String fieldName = randomRealisticUnicodeOfCodepointLengthBetween(1, 10);
+                    if (fieldName.isBlank()) {
+                        continue;
+                    }
+                    if (fieldName.indexOf('.') != -1) {
+                        continue;
+                    }
+
+                    return fieldName;
+                }
             }
         };
     }

test/framework/src/main/java/org/elasticsearch/datageneration/datasource/DefaultPrimitiveTypesHandler.java

@@ -59,7 +59,7 @@ public DataSourceResponse.HalfFloatGenerator handle(DataSourceRequest.HalfFloatG
 
     @Override
     public DataSourceResponse.StringGenerator handle(DataSourceRequest.StringGenerator request) {
-        return new DataSourceResponse.StringGenerator(() -> ESTestCase.randomAlphaOfLengthBetween(0, 50));
+        return new DataSourceResponse.StringGenerator(() -> ESTestCase.randomRealisticUnicodeOfCodepointLengthBetween(0, 50));
     }
 
     @Override