feat: 完善demo机制；实现tab的demo和var标签的demo；

extend/base/admin/view/index/ext/admin_menu_tab_content_demo.html

@@ -0,0 +1,12 @@
+<div lay-id="layuiminiDemoTabIdContent" class="layui-tab-item">
+
+    <!-- var的用法，如果变量未声明，则声明，比如a1 -->
+    {var name='a1' value='a1' /}
+    {$a1}
+    <!-- 如果变量早已声明，则不生效，比如a2，在extend\base\common\event\AdminMenuTab\DemoEventBase.php定义了 -->
+    {var name='a2' value='a2' /}
+    {$a2}
+    <!-- 与assign区别，即便其他地方已经定义了a3，此处仍然会被定义 -->
+    {assign name='a3' value='a3' /}
+    {$a3}
+</div>

extend/base/admin/view/index/ext/admin_menu_tab_demo.html

@@ -1 +1 @@
-<!-- <li id="layuiminiDemoTabId" lay-id="">演示用例</li> -->
+<li id="layuiminiDemoTabId" lay-id="layuiminiDemoTabIdContent">演示用例</li>

extend/base/admin/view/index/index.html

@@ -118,6 +118,7 @@
                     {else /}
                     <div id="layuiminiHomeTabIframe" class="layui-tab-item layui-show"></div>
                     {/if}
+                    {:event_handle_string('AdminMenuTab','tab_content')}
                 </div>
             </div>
         </div>

extend/base/common/event/AdminMenuTab/DemoEventBase.php

@@ -10,14 +10,20 @@ class DemoEventBase
     public function handle()
     {
         $content = '';
-        
+        $tab_content = '';
+
         if (Env::get('adminsystem.is_demo', false)) {
             $content = View::layout(false)->fetch('index/ext/admin_menu_tab_demo');
+            $tab_content = View::layout(false)->fetch('index/ext/admin_menu_tab_content_demo');
         }
 
+        View::assign('a2','x2');
+        View::assign('a3','x3');
         // 事件监听处理
         return [
             'view_content' => $content,
+            // AdminMenuTab专有的扩展字段
+            'tab_content' => $tab_content,
         ];
     }
 }