[FEATURE] youtube翻译请求加载时保留原字幕显示

[littlehappy123456]

Before you begin

• I have searched existing issues to avoid duplicates
• I am willing to contribute a PR for this feature

Is your feature request related to a problem? Please describe.

当youtube翻译请求加载时，原字幕会彻底消失，取而代之的是视频左下角的“Read Frog 字幕加载中”。
这样有几个不好的地方：
1.当api响应缓慢时，需要等待比较长的时间才能看到字幕。而有时候翻译的字幕只是作为一种辅助手段去帮助理解，原字幕的大致内容还是看得懂的。
2.学习场景：当想回退视频查看相应的句子和单词时，无法及时获取

Describe the solution you'd like

当youtube翻译请求加载时，保留原字幕，响应成功后再补上翻译的字幕

Which area(s) would this feature affect? (Select all that apply)

Browser Extension, Website

Additional context

No response

[taiiiyang]

我们调整下设计，让原字幕和加载中一起显示