fix readpixels

[zhakesi]

1] 修复高度设置错误
2] 添加接收像素buffer参数

• https://github.com/cocos-creator/3d-tasks/issues/10543

[github-actions]

Interface Check Report

! WARNING this pull request has changed these public interfaces:

@@ -15957,10 +15957,11 @@
          * @param x 起始位置X轴坐标
          * @param y 起始位置Y轴坐标
          * @param width 像素宽度
          * @param height 像素高度
+         * @param buffer 像素缓存
          */
-        readPixels(x?: number, y?: number, width?: number, height?: number): Uint8Array | null;
+        readPixels(x?: number, y?: number, width?: number, height?: number, buffer?: Uint8Array): Uint8Array | null;
     }
     /**
      * @en The script asset base class
      * @zh 脚本资源基类。