Attach to non-files

[rwols]

Is your feature request related to a problem? Please describe.
I would like to see language servers attached to views without filenames.

Describe the solution you'd like
Attach to any view whose base scope matches the selector.

Additional context
Motivated by new views created ad-hoc with CTRL+N.
And motivated by language servers that understand a custom scheme like deno: or json-schema:.
One problem is that we should probably first listen for setting changes in the view to keep an eye on the current syntax.

[rwols]

Also, some external packages like Debugger would need to know the URI of a view as well, so it would probably have to go into the settings object.