add newBuilder() to logging.SourceLocation (#3339)

* add newBuilder() to logging.SourceLocation

* fix code review

Author: yihanzhen

google-cloud-clients/google-cloud-logging/src/main/java/com/google/cloud/logging/SourceLocation.java

@@ -33,6 +33,10 @@ public final class SourceLocation implements Serializable {
   private final Long line;
   private final String function;
 
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
   /**
    * A builder for {@code SourceLocation} objects.
    */

google-cloud-clients/google-cloud-logging/src/test/java/com/google/cloud/logging/SourceLocationTest.java

@@ -25,7 +25,7 @@ public class SourceLocationTest {
   private static final String FILE = "file";
   private static final Long LINE = 42L;
   private static final String FUNCTION = "function";
-  private static final SourceLocation SOURCE_LOCATION = new SourceLocation.Builder()
+  private static final SourceLocation SOURCE_LOCATION = SourceLocation.newBuilder()
       .setFile(FILE)
       .setLine(LINE)
       .setFunction(FUNCTION)