Restore context ClassLoader management during plugin lifecycle (#7746)

#### What type of PR is this?

/kind improvement
/area plugin
/milestone 2.21.x

#### What this PR does / why we need it:

This PR restores context ClassLoader mangement during plugin lifecycle to prevent resource leak.

Meanwhile, it also fixes Class initialization error when starting plugins.

Superseds #7725

#### Does this PR introduce a user-facing change?

```release-note
None
```

Author: JohnNiang

application/src/main/java/run/halo/app/plugin/DefaultPluginApplicationContextFactory.java

@@ -70,11 +70,6 @@ public ApplicationContext create(String pluginId) {
         var pluginWrapper = pluginManager.getPlugin(pluginId);
         var classLoader = pluginWrapper.getPluginClassLoader();
 
-        // Set the context ClassLoader to the plugin ClassLoader to ensure that
-        // any class loading operations performed by the context (e.g., initializing
-        // bean definitions, loading class resources during static initialization)
-        // use the correct ClassLoader.
-        Thread.currentThread().setContextClassLoader(classLoader);
 
         /*
          * Manually creating a BeanFactory and setting the plugin's ClassLoader is necessary
@@ -189,7 +184,18 @@ public ApplicationContext create(String pluginId) {
         log.debug("Refreshing application context for plugin {}", pluginId);
         sw.start("Refresh");
 
-        context.refresh();
+        // Set the context ClassLoader to the plugin ClassLoader to ensure that
+        // any class loading operations performed by the context (e.g., initializing
+        // bean definitions, loading class resources during static initialization)
+        // use the correct ClassLoader.
+        var previous = Thread.currentThread().getContextClassLoader();
+        try {
+            Thread.currentThread().setContextClassLoader(classLoader);
+            context.refresh();
+        } finally {
+            // reset the class loader to previous one to prevent resource leak
+            Thread.currentThread().setContextClassLoader(previous);
+        }
         sw.stop();
         log.debug("Refreshed application context for plugin {}", pluginId);
         if (log.isDebugEnabled()) {

application/src/main/java/run/halo/app/plugin/SpringPlugin.java

@@ -27,9 +27,11 @@ public SpringPlugin(PluginApplicationContextFactory contextFactory,
     public void start() {
         log.info("Preparing starting plugin {}", pluginContext.getName());
         var pluginId = pluginContext.getName();
+        var previous = Thread.currentThread().getContextClassLoader();
         try {
             // initialize context
             this.context = contextFactory.create(pluginId);
+            Thread.currentThread().setContextClassLoader(this.context.getClassLoader());
             log.info("Application context {} for plugin {} is created", this.context, pluginId);
 
             var pluginOpt = context.getBeanProvider(Plugin.class)
@@ -55,13 +57,17 @@ public void start() {
             this.stop();
             // propagate exception to invoker.
             throw t;
+        } finally {
+            Thread.currentThread().setContextClassLoader(previous);
         }
     }
 
     @Override
     public void stop() {
+        var previous = Thread.currentThread().getContextClassLoader();
         try {
             if (context != null) {
+                Thread.currentThread().setContextClassLoader(context.getClassLoader());
                 log.info("Before publishing plugin stopping event for plugin {}",
                     pluginContext.getName());
                 context.publishEvent(new SpringPluginStoppingEvent(this, this));
@@ -74,6 +80,7 @@ public void stop() {
                 log.info("Stopped {} for plugin {}", this.delegate, pluginContext.getName());
             }
         } finally {
+            Thread.currentThread().setContextClassLoader(previous);
             if (context instanceof ConfigurableApplicationContext configurableContext) {
                 log.info("Closing plugin context for plugin {}", pluginContext.getName());
                 configurableContext.close();