Move plugin classloader to its own package (#73786)

The plugin classloader exists in its own jar file for legacy reasons,
and while it should go away in the future, it currently duplicates the
package name of the rest of the plugin classes. This commit moves the
classloader into its own unique package.

relates #73784

Author: rjernst

libs/plugin-classloader/src/main/java/org/elasticsearch/plugins/ExtendedPluginsClassLoader.java renamed to libs/plugin-classloader/src/main/java/org/elasticsearch/plugins/loader/ExtendedPluginsClassLoader.java

@@ -6,7 +6,7 @@
  * Side Public License, v 1.
  */
 
-package org.elasticsearch.plugins;
+package org.elasticsearch.plugins.loader;
 
 import java.security.AccessController;
 import java.security.PrivilegedAction;

server/src/main/java/org/elasticsearch/plugins/PluginLoaderIndirection.java

@@ -8,6 +8,8 @@
 
 package org.elasticsearch.plugins;
 
+import org.elasticsearch.plugins.loader.ExtendedPluginsClassLoader;
+
 import java.util.List;
 
 // TODO: remove this indirection now that transport client is gone

test/framework/src/main/java/org/elasticsearch/bootstrap/BootstrapForTesting.java

@@ -179,7 +179,7 @@ static Map<String, URL> getCodebases() {
         Map<String, URL> codebases = PolicyUtil.getCodebaseJarMap(JarHell.parseClassPath());
         // when testing server, the main elasticsearch code is not yet in a jar, so we need to manually add it
         addClassCodebase(codebases,"elasticsearch", "org.elasticsearch.plugins.PluginsService");
-        addClassCodebase(codebases,"elasticsearch-plugin-classloader", "org.elasticsearch.plugins.ExtendedPluginsClassLoader");
+        addClassCodebase(codebases,"elasticsearch-plugin-classloader", "org.elasticsearch.plugins.loader.ExtendedPluginsClassLoader");
         addClassCodebase(codebases,"elasticsearch-nio", "org.elasticsearch.nio.ChannelFactory");
         addClassCodebase(codebases, "elasticsearch-secure-sm", "org.elasticsearch.secure_sm.SecureSM");
         addClassCodebase(codebases, "elasticsearch-rest-client", "org.elasticsearch.client.RestClient");