zh-cn: proofreading and update html Multimedia and embedding section

[hanyujie2002]

I plan to proofread and update the translation of Multimedia and embedding section

Tasks

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1. Multimedia and embedding zh-cn: translate multimedia and embedding #18314
2. Images in HTML in [zh-cn]: revise the translation of images in html #18812
3. Video and audio content in zh-cn: revise the translation of "Video and audio content" #19210
4. From object to iframe — other embedding technologies in zh-cn: revise the translation of other embedding technologies #19569
5. Adding vector graphics to the web in [zh-cn] update the translation of "Adding vector graphics to the web" #19617
6. Responsive images in zh-cn: revise the translation of "responsive image" #19746
7. Mozilla splash page in zh-cn: revise the translation of "splash page" #19919

[hanyujie2002]

All tasks done. Thank you very much ❤ @yin1999 @jasonren0403