Add Main-Class for cpp-build tools JAR.

- Adds the manifest entries to the basic tools JAR.

- Creates a symlink named like the dependencies JAR that was used
  previously.

- Creates a symlink to the protobuf JAR.

In the manifest, the classpath reference to the protobuf JAR is a
relative filename. The second symbolic link satisfies that by linking to
the installed JAR.

This is only needed for people building packages

People who build normally with Maven will find that "mvn package" still
produces the original tools JAR which has its own Main-Class attribute

Author: daniel@pocock.pro

debian/rules

@@ -62,6 +62,8 @@ configure/libphonenumber6::
 #	ln -s /usr/share/java/junit4.jar java/lib/junit-4.8.1.jar
 #	$(ANT) -f $(JAVA_BUILD).xml jar
 build/libphonenumber6::
+	ln -sf cpp-build-1.0-SNAPSHOT.jar tools/java/cpp-build/target/cpp-build-1.0-SNAPSHOT-jar-with-dependencies.jar
+	ln -sf /usr/share/java/protobuf.jar tools/java/cpp-build/target/protobuf-java-debian.jar
 	$(MAKE) -C $(CPP_BUILD) phonenumber phonenumber-shared
 
 #override_dh_auto_test:

tools/java/cpp-build/pom.xml

@@ -91,6 +91,18 @@
           </arguments>
         </configuration>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <configuration>
+          <archive>
+            <manifest>
+              <addClasspath>true</addClasspath>
+              <mainClass>com.google.i18n.phonenumbers.EntryPoint</mainClass>
+            </manifest>
+          </archive>
+        </configuration>
+      </plugin>
       <!-- Build a JAR with its dependencies (protocol buffers and common library). This JAR
            contains the C++ build tools invoked by CMake during the libphonenumber C++ build. -->
       <plugin>