Use .css instead of .scss in property lists

[winstliu]

This change brings language-sass in line with language-css and language-less. The main goal of this PR is to allow for deduplication in autocomplete-css.

[winstliu]

/cc @esdoppio for language review, @simurai for styling. There shouldn't be anything explicitly targeting the .scss variant, right?

[hediyi]

Theoretically, I think "meta.property-list.scss" should remain as it is, because unlike property-name or property-value, what can go into a "property list" (still don't like the name) of SCSS is very different from that of CSS. But other than that, I don't see why we can't change it.

[simurai]

👍 with this.

I don't think themes want style properties differently in SCSS vs CSS. And I think they still can with a more specific selector, like .source.scss xxx.css.

[winstliu]

Alternatively, we could use meta.property-list.css.scss. Any thoughts about that?

[simurai]

Yeah, I guess having both (.css.scss) would lower the chance of breaking anything.