[fix][fn]make sure the classloader for ContextImpl is `functionClassL…

…oader` in different runtimes (#22501)

(cherry picked from commit d067efc)

pulsar-functions/instance/src/main/java/org/apache/pulsar/functions/instance/JavaInstanceRunnable.java

@@ -272,9 +272,15 @@ private synchronized void setup() throws Exception {
     ContextImpl setupContext() throws PulsarClientException {
         Logger instanceLog = LoggerFactory.getILoggerFactory().getLogger(
                 "function-" + instanceConfig.getFunctionDetails().getName());
-        return new ContextImpl(instanceConfig, instanceLog, client, secretsProvider,
+        ClassLoader clsLoader = Thread.currentThread().getContextClassLoader();
+        try {
+            Thread.currentThread().setContextClassLoader(functionClassLoader);
+            return new ContextImpl(instanceConfig, instanceLog, client, secretsProvider,
                 collectorRegistry, metricsLabels, this.componentType, this.stats, stateManager,
                 pulsarAdmin, clientBuilder);
+        } finally {
+            Thread.currentThread().setContextClassLoader(clsLoader);
+        }
     }
 
     public interface AsyncResultConsumer {