Remove scheme restriction for Markdown/Emmet language features

[lostintangent]

This PR simply removes the scheme restriction from the Markdown and Emmet extension's language features. This allows these features to apply to virtual file systems (e.g. GistPad, in addition to just local files and untitled files. I tested all of these features in local files, non-file based files, as well as within a Live Share session, and everything works as expected 👍

Fixed #87859

// CC @mattbierner

[mjbvz]

Thanks for the PR.

Can you check the dev tools console too after loading a markdown fold with this change. I think using document selectors without schemes may generate a warning

@jrieken may know more about this

[lostintangent]

Will do! If you’re cool with it, I can also change to using arrays of Ianguage IDs, instead of the object selector format.

[jrieken]

I think using document selectors without schemes may generate a warning

Yes, unless you are explicit e.g via scheme: '*'. That will tell us that you have thought about the situation.

[lostintangent]

@jrieken @mjbvz Just pushed an update that explicitly states the * scheme 👍

[mjbvz]

@lostintangent Markdown change looks good to me.

Can you also please create an issue for this so that we can link it to the Jan milestone and properly verify it

[lostintangent]

@mjbvz Done! #87859.