theme: Include both dark and light variant in resource

This will allow us to switch between the variants according to
the color-scheme setting.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5545

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2324>

data/theme/gnome-shell-light.scss

@@ -0,0 +1,6 @@
+$variant: 'light';
+
+@import "gnome-shell-sass/_colors"; //use gtk colors
+@import "gnome-shell-sass/_drawing";
+@import "gnome-shell-sass/_common";
+@import "gnome-shell-sass/_widgets";

data/theme/meson.build

@@ -1,6 +1,7 @@
 theme_sources = files([
   'gnome-shell-high-contrast.scss',
-  'gnome-shell.scss',
+  'gnome-shell-dark.scss',
+  'gnome-shell-light.scss',
   'gnome-shell-sass/_colors.scss',
   'gnome-shell-sass/_common.scss',
   'gnome-shell-sass/_drawing.scss',
@@ -43,7 +44,8 @@ theme_sources = files([
 
 stylesheets = [
   'gnome-shell-high-contrast.css',
-  'gnome-shell.css'
+  'gnome-shell-dark.css',
+  'gnome-shell-light.css',
 ]
 
 foreach stylesheet: stylesheets