apacheGH-44016: [Java] Consider warnings as errors for Format Module (a…

…pache#44017)

### Rationale for this change

This PR configs the build such that warnings are considered errors in the Format module. And corresponding code changes have also been made.

### What changes are included in this PR?

Adding flags to consider warnings as errors in javac and fixing the corresponding errors.

### Are these changes tested?

Tested by existing test cases.

### Are there any user-facing changes?

N/A
* GitHub Issue: apache#44016

Lead-authored-by: Vibhatha Lakmal Abeykoon <[email protected]>
Co-authored-by: Vibhatha Lakmal Abeykoon <[email protected]>
Co-authored-by: David Li <[email protected]>
Signed-off-by: Dane Pitkin <[email protected]>

java/format/pom.xml

@@ -61,6 +61,15 @@ under the License.
           </java>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <configuration combine.children="append">
+          <compilerArgs>
+            <arg>-Werror</arg>
+          </compilerArgs>
+        </configuration>
+      </plugin>
     </plugins>
   </build>
 </project>

java/format/src/main/java/module-info.java

@@ -15,6 +15,8 @@
  * limitations under the License.
  */
 
+// TODO(https://github.com/apache/arrow/issues/44037): Google hasn't reviewed Flatbuffers fix
+@SuppressWarnings({ "requires-automatic", "requires-transitive-automatic" })
 module org.apache.arrow.format {
   exports org.apache.arrow.flatbuf;
   requires transitive flatbuffers.java;