[AMQ-9777] Migrate to using multi-release jar for activemq-client

Author: mattrpav

activemq-client-jdk21-test/pom.xml

@@ -200,15 +200,21 @@
         <configuration>
           <instructions>
             <Import-Package>
+              !java.*,
+              !javax.naming*,
+              !javax.net*,
+              !org.apache.activemq*,
               !com.google.errorprone.annotations,
               !com.google.errorprone.annotations.concurrent,
               com.thoughtworks.xstream.*;resolution:="optional",
+              javax.jmdns.*;resolution:="optional",
               *
             </Import-Package>
             <Private-Package>
               com.google.errorprone.annotations,
               com.google.errorprone.annotations.concurrent
             </Private-Package>
+            <Multi-Release>true</Multi-Release>
             <_noee>true</_noee>
           </instructions>
         </configuration>
@@ -396,5 +402,32 @@
         </plugins>
       </build>
     </profile>
+    <profile>
+      <id>jdk21-plus</id>
+      <activation>
+        <jdk>[21,)</jdk>
+      </activation>
+      <build>
+        <plugins>
+          <plugin>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <executions>
+              <execution>
+                <id>java21-compile</id>
+                <phase>compile</phase>
+                <goals>
+                  <goal>compile</goal>
+                </goals>
+                <configuration>
+                  <release>21</release> <!-- Specific Java version for alternative classes -->
+                  <compileSourceRoots>${project.basedir}/src/main/java21</compileSourceRoots>
+                  <multiReleaseOutput>true</multiReleaseOutput>
+                </configuration>
+              </execution>
+            </executions>
+          </plugin>
+        </plugins> 
+      </build>
+    </profile>
   </profiles>
 </project>