Support for youtube video subtitles

[xyaman]

This adds support for in-video subtitles and also works with ASR. The code is still messy, but it works. I'm just sharing it here so that other people can maybe help as well.

While non-ASR subtitles work perfectly, there are some issues with ASR.

Current limitations:

• ASR support is poor. Youtube ASR timestamps are designed to be displayed continuously instead of as "blocks" of subtitles. To avoid making a large number of calls to the jpdb API, I performed some preprocessing on the captions, but the result is still not very good.
• ASR subtitles try to mimic real YouTube subtitles, but currently, they don't look and behave exactly like real YouTube subtitles.

TODO:

• Handle errors properly.

• Code refactoring.

• Parse subtitles before displaying.

• Might be good idea to split the code, I had some problems with the extension when I tried ('export' not defined), maybe someone else can figure it out.

• Don't merge it yet!

[max-kamps]

Might be good idea to split the code, I had some problems with the extension when I tried ('export' not defined), maybe someone else can figure it out.

Should probably improve the error message for that... :smile: If you want to split part of a content script into a separate file, you need to make that file a normal module (i.e. remove the // @reader content-script comment.) Like how integrations/common.ts does it.