general: add roboto slab (#31009)

README

@@ -134,6 +134,13 @@ copyright notices:
   #
   # https://www.fontsquirrel.com/license/archivo-narrow
 
+* Roboto Slab
+  # Font data copyright Google 2013
+  #
+  # Apache License
+  #
+  # https://www.fontsquirrel.com/license/roboto-slab
+
 ~~~~
 
 Some theme variant files have their own specific licenses; refer to

static/includes/_font-roboto-slab.scss

@@ -0,0 +1,14 @@
+@mixin robotoslab-font($type, $weight) {
+	@font-face {
+		font-family: 'Roboto Slab';
+		src: url('../fonts/RobotoSlab/robotoslab-#{$type}-webfont.woff2') format('woff2'),
+		     url('../fonts/RobotoSlab/robotoslab-#{$type}-webfont.woff') format('woff');
+		font-weight: $weight;
+		font-style: normal;
+	}
+}
+
+@include robotoslab-font('thin', 200);
+@include robotoslab-font('light', 300);
+@include robotoslab-font('regular', 400);
+@include robotoslab-font('bold', 700);