add douyin (chinese tiktok) support

[pumpkies]

https://www.douyin.com/

sample links

https://v.douyin.com/iysEh9UH/
https://v.douyin.com/iysE2VFv/
https://v.douyin.com/iysEsLXA/ 
https://v.douyin.com/iysE5YXK/

[Pandas886]

need it

[a1exsun]

really need it

[wukko]

you're welcome to make a pull request

[Yumega]

really really need it

[jearton]

need it + 1

[ihatespawn]

if you need it then maybe you should make a pull request so it will be in cobalt faster