Move component .js-enabled styling to .govuk-frontend-supported

This closes the support gap for browsers without ES module support still loading JavaScript-only styles

src/stylesheets/components/_back-to-top.scss

@@ -12,14 +12,14 @@
     margin-bottom: govuk-spacing(8);
   }
 
-  .js-enabled .app-back-to-top--fixed {
+  .govuk-frontend-supported .app-back-to-top--fixed {
     position: fixed;
     top: calc(100% - #{govuk-spacing(8)});
     bottom: auto;
     left: auto;
   }
 
-  .js-enabled .app-back-to-top--hidden .app-back-to-top__link {
+  .govuk-frontend-supported .app-back-to-top--hidden .app-back-to-top__link {
     @include govuk-visually-hidden-focusable;
   }
 }

src/stylesheets/components/_navigation.scss

@@ -78,12 +78,12 @@
   list-style: none;
 }
 
-.js-enabled .app-navigation__subnav--active {
+.govuk-frontend-supported .app-navigation__subnav--active {
   display: block;
 }
 
 .app-navigation__subnav,
-.js-enabled .app-navigation__subnav--active {
+.govuk-frontend-supported .app-navigation__subnav--active {
   @include govuk-media-query($from: tablet) {
     display: none;
   }

src/stylesheets/components/_site-search.scss

@@ -21,7 +21,7 @@ $icon-size: 40px;
   margin-bottom: govuk-spacing(2);
   float: left;
 
-  .js-enabled & {
+  .govuk-frontend-supported & {
     display: block;
   }
 
@@ -37,7 +37,7 @@ $icon-size: 40px;
     float: right;
     text-align: right;
 
-    .js-enabled & {
+    .govuk-frontend-supported & {
       text-align: left;
     }
   }
@@ -205,7 +205,7 @@ $icon-size: 40px;
   @include govuk-media-query($from: tablet) {
     display: inline-block;
 
-    .js-enabled & {
+    .govuk-frontend-supported & {
       display: none;
     }
   }

src/stylesheets/main.scss

@@ -286,7 +286,7 @@ pre code {
     outline: $govuk-focus-width solid $govuk-focus-colour;
   }
 
-  .js-enabled [data-module="app-copy"] & {
+  .govuk-frontend-supported [data-module="app-copy"] & {
     padding-top: 45px; // Allow extra space for the copy code button
   }
 }