fix(gen_stub): use toVarEscapedName for union type ZEND_TYPE_INIT_CLASS

When generating arginfo for union/intersection types with 2+ class types,
the ZEND_TYPE_INIT_CLASS macro was using toEscapedName() which preserves
backslashes (e.g. yuandian\\Database\\Db\\Expression\\Raw), but
C identifiers cannot contain backslashes.

This caused compilation errors like:
  error: stray '\' in program

Fix: use toVarEscapedName() which replaces namespace separators with
underscores, consistent with the single-class-type branch (line 2901).

src/gen_stub.php

@@ -2881,8 +2881,8 @@ abstract class VariableLike
                     $code .= "\t{$variableLikeType}_{$variableLikeName}_type_list->num_types = $classTypeCount;\n";
 
                     foreach ($arginfoType->classTypes as $k => $classType) {
-                        $escapedClassName = $classType->toEscapedName();
-                        $code .= "\t{$variableLikeType}_{$variableLikeName}_type_list->types[$k] = (zend_type) ZEND_TYPE_INIT_CLASS({$variableLikeType}_{$variableLikeName}_class_{$escapedClassName}, 0, 0);\n";
+                        $varEscapedClassName = $classType->toVarEscapedName();
+                        $code .= "\t{$variableLikeType}_{$variableLikeName}_type_list->types[$k] = (zend_type) ZEND_TYPE_INIT_CLASS({$variableLikeType}_{$variableLikeName}_class_{$varEscapedClassName}, 0, 0);\n";
                     }
 
                     $typeMaskCode = $this->type->toArginfoType()->toTypeMask();