Move .bg-* utility classes into separate file

[skip sauce]
[skip validator]

scss/_utilities-background.scss

+//
+// Contextual backgrounds
+//
+
+// Inverse
+// TODO: redo this as a proper class
+.bg-inverse {
+  color: $gray-lighter;
+  background-color: $gray-dark;
+}
+
+.bg-faded {
+  background-color: $gray-lightest;
+}
+
+@include bg-variant('.bg-primary', $brand-primary);
+
+@include bg-variant('.bg-success', $brand-success);
+
+@include bg-variant('.bg-info', $brand-info);
+
+@include bg-variant('.bg-warning', $brand-warning);
+
+@include bg-variant('.bg-danger', $brand-danger);

scss/_utilities.scss

@@ -89,29 +89,3 @@
 @include text-emphasis-variant('.text-warning', $brand-warning);
 
 @include text-emphasis-variant('.text-danger', $brand-danger);
-
-
-// Contextual backgrounds
-// For now we'll leave these alongside the text classes until v4 when we can
-// safely shift things around (per SemVer rules).
-
-// Inverse
-// Todo: redo this as a proper class
-.bg-inverse {
-  color: $gray-lighter;
-  background-color: $gray-dark;
-}
-
-.bg-faded {
-  background-color: $gray-lightest;
-}
-
-@include bg-variant('.bg-primary', $brand-primary);
-
-@include bg-variant('.bg-success', $brand-success);
-
-@include bg-variant('.bg-info', $brand-info);
-
-@include bg-variant('.bg-warning', $brand-warning);
-
-@include bg-variant('.bg-danger', $brand-danger);

scss/bootstrap.scss

@@ -51,5 +51,6 @@
 
 // Utility classes
 @import "utilities";
+@import "utilities-background";
 @import "utilities-spacing";
 @import "utilities-responsive";