Migrate Iceberg ApplyChangeLog to connector function

Move ApplyChangelogFunction from IcebergPlugin.getFunctions() to
IcebergConnector.getSystemFunctions() to make it available in the
iceberg.system namespace instead of presto.default namespace.

This follows the connector-level function pattern introduced in PR prestodb#25594
and improves function organization by keeping connector-specific
functions within their appropriate namespaces.

The function behavior remains unchanged – only the namespace changes
from presto.default to iceberg.system.

Resolves: prestodb#25849

Add test for ApplyChangeLog function in connector namespace

Add tests to TestIcebergTableChangelog to verify that the apply_changelog
function is correctly available in the iceberg.system namespace and
no longer accessible in the global or presto.default namespaces.

This ensures the migration from IcebergPlugin.getFunctions() to
IcebergConnector.getSystemFunctions() works as expected.

Author: MinuteHanD

presto-iceberg/src/main/java/com/facebook/presto/iceberg/IcebergConnector.java

@@ -15,6 +15,7 @@
 
 import com.facebook.airlift.bootstrap.LifeCycleManager;
 import com.facebook.presto.hive.HiveTransactionHandle;
+import com.facebook.presto.iceberg.function.changelog.ApplyChangelogFunction;
 import com.facebook.presto.spi.SystemTable;
 import com.facebook.presto.spi.classloader.ThreadContextClassLoader;
 import com.facebook.presto.spi.connector.Connector;
@@ -218,4 +219,12 @@ public ConnectorPlanOptimizerProvider getConnectorPlanOptimizerProvider()
     {
         return planOptimizerProvider;
     }
+
+    @Override
+    public Set<Class<?>> getSystemFunctions()
+    {
+        return ImmutableSet.<Class<?>>builder()
+                .add(ApplyChangelogFunction.class)
+                .build();
+    }
 }

presto-iceberg/src/main/java/com/facebook/presto/iceberg/IcebergPlugin.java

@@ -13,16 +13,13 @@
  */
 package com.facebook.presto.iceberg;
 
-import com.facebook.presto.iceberg.function.changelog.ApplyChangelogFunction;
 import com.facebook.presto.spi.Plugin;
 import com.facebook.presto.spi.connector.ConnectorFactory;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableSet;
 
 import javax.management.MBeanServer;
 
 import java.lang.management.ManagementFactory;
-import java.util.Set;
 
 public class IcebergPlugin
         implements Plugin
@@ -44,12 +41,4 @@ public Iterable<ConnectorFactory> getConnectorFactories()
     {
         return ImmutableList.of(new IcebergConnectorFactory(mBeanServer));
     }
-
-    @Override
-    public Set<Class<?>> getFunctions()
-    {
-        return ImmutableSet.<Class<?>>builder()
-                .add(ApplyChangelogFunction.class)
-                .build();
-    }
 }

presto-iceberg/src/test/java/com/facebook/presto/iceberg/TestIcebergTableChangelog.java

@@ -308,4 +308,28 @@ private long getSnapshot(int idx, String tableName)
                 .mapToLong(Long.class::cast)
                 .skip(idx).findFirst().getAsLong();
     }
+
+    @Test
+    public void testApplyChangelogFunctionInSystemNamespace()
+    {
+        assertQuery(
+                "SELECT iceberg.system.apply_changelog(1, 'INSERT', 'test_value') IS NOT NULL",
+                "SELECT true");
+    }
+
+    @Test
+    public void testApplyChangelogFunctionNotInGlobalNamespace()
+    {
+        assertQueryFails(
+                "SELECT apply_changelog(1, 'INSERT', 'test_value')",
+                "line 1:8: Function apply_changelog not registered");
+    }
+
+    @Test
+    public void testApplyChangelogFunctionNotInPrestoDefaultNamespace()
+    {
+        assertQueryFails(
+                "SELECT presto.default.apply_changelog(1, 'INSERT', 'test_value')",
+                "line 1:8: Function apply_changelog not registered");
+    }
 }