Add subtitles to live demos in React 18 Concurrency talk

[vadikmash]

Added subtitles to Live Demos in React 18 Concurrency talk!

Subtitles were generated with openai/whisper using medium model and then manually edited by me. Please, let me know if I missed or misheard something.

Here are originally generated subtitles. Just in case.

Unfortunately I weren't able to import subtitles without webpack's inline loader syntax. @iamakulov, I wonder if you know how to do this.

/* eslint-disable import/order */
/* eslint-disable import/no-unresolved */
import subtitlesDemo1 from 'file-loader!./live-demos/subtitles/demo1.mp4.vtt';
import subtitlesDemo3 from 'file-loader!./live-demos/subtitles/demo3.mp4.vtt';
import subtitlesDemo4 from 'file-loader!./live-demos/subtitles/demo4.mp4.vtt';
import subtitlesDemo5 from 'file-loader!./live-demos/subtitles/demo5.mp4.vtt';
/* eslint-disable import/no-unresolved */
/* eslint-disable import/order */

As a bonus, I also did a couple of super-minor fixes/improvements in a couple of files. Take a look at changed files for details.

[iamakulov]

Thank you!!