fix(aot): 修复空合并赋值运算符测试用例和类名解析问题

- 更新测试用例 004.phpt 中的变量初始化顺序以匹配预期行为
- 修改 CompilerBase.php 中的类名解析逻辑，使用 getFullClassName() 替代直接访问 $this->class
- 确保 self 引用时获取完整的类名信息

src/Php/CompilerBase.php

@@ -4014,7 +4014,7 @@ class CompilerBase extends \PhpAot\Core\Translator
             $class = $this->parseIdentifier($expr->class);
             $propertyName = $this->parseIdentifier($expr->name);
             if ($class === 'self') {
-                $class = $this->class;
+                $class = $this->getFullClassName();
             } elseif ($class === 'parent') {
                 if (!$this->classDef->extends) {
                     $this->fatalError($expr, 'Cannot access parent:: when current class does not extend any class');

tests/aot/coalesce/004.phpt

@@ -3,16 +3,19 @@ Test ?? operator
 --FILE--
 <?php
 function foo1() {
+    $a = null;
+    $b = null;
     $c = 100;
-    $a ??=  $b ??= $c;
+    $a ??= $b ??= $c;
     var_dump($a, $b);
 
 }
 
 function foo2() {
-    $c = 100;
+    $a = null;
     $b = 33;
-    $a ??=  $b ??= $c;
+    $c = 100;
+    $a ??= $b ??= $c;
     var_dump($a, $b);
 }