Enable error level for the DefaultPackage bug pattern in ErrorProne

Ignore the current issues so that the build continues to work:

* The Main class is supposed to be in the default package.

* For the generated TestSuite classes we don't care in which package
  they are. Ideally they would be in the same package as the test
  classes, but my Bazel skills are not sufficient to tweak
  tools/bzl/junit.bzl to achieve this. If someone is passionate about
  this, they may fix this later.

Bug: Issue 15060
Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I77a89e134ae8d7824d2186f215d6286b12d7ed30

java/Main.java

diff --git a/java/Main.java b/java/Main.java
index 11d8234..09c8c76 100644
--- a/java/Main.java
+++ b/java/Main.java
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+@SuppressWarnings("DefaultPackage")
 public final class Main {
   private static final String FLOGGER_BACKEND_PROPERTY = "flogger.backend_factory";
   private static final String FLOGGER_LOGGING_CONTEXT = "flogger.logging_context";