[Feat] Add IntelliSense support for custom media queries

[webschik]

Hi, thank you for developing this great extension!

It would amazing if it could support "Autocomplete" and "Go to definition" functionality for custom media queries:

@custom-media --small-viewport-max-width (max-width: 767px);
@custom-media --medium-viewport-min-width (min-width: 768px);