feat: element filter (whitelist/blacklist) (user-configured)

[WofWca]

This is similar to #26, but offers a different, more generic approach (this can be a superset of #26).

We could add an option that works like a filter function. It is executed for every media (audio/video) element. The API is like this:

type Filter = (context: { srcUrl: URL, pageUrl: URL, element: HTMLMediaElement }) => boolean

If the return value is true, then we attach to the element, otherwise not.

We need to make it accessible to users though, and make sure that it's hard (impossible?) to execute arbitrary code there, in case someone decided to copy-paste the filters from somewhere.
Though initially we could implement a simplistic version, accessible by advanced users only (say, through the console).

I'm sure this task or similar has been solved already and there are available solutions / filtering languages. First thing that comes to mind is adblocker extension rules, like in uBlock Origin.