Configure builds

- Create `dartsass.builds` initializer and add all Sass files to be compiled. See https://github.com/rails/dartsass-rails#configuring-builds
- Create .keep
- Update manifest file to use /builds directory
- Ignore /builds

Author: jon-kirwan

.gitignore

@@ -9,6 +9,8 @@ log/*.log
 tmp/
 coverage
 public/assets
+/app/assets/builds/*
+!/app/assets/builds/.keep
 node_modules
 yarn-error.log
 spec/reports/pacts

app/assets/builds/.keep

@@ -2,25 +2,5 @@
 //= link all.js
 //= link application.js
 //= link test-dependencies.js
-//= link application.css
 
-//= link components/_calendar.css
-//= link components/_metadata.css
-//= link components/_subscribe.css
-
-//= link views/_calendars.css
-//= link views/_cookie-settings.css
-//= link views/_csv_preview.css
-//= link views/_homepage.css
-//= link views/_homepage_new.css
-//= link views/_travel-advice.css
-//= link views/_report-child-abuse.css
-//= link views/_inverse_header.css
-//= link views/_homepage_header.css
-
-//= link views/_local-transaction.css
-//= link views/_location_form.css
-//= link views/_links_and_search.css
-//= link views/_popular_links.css
-//= link views/_homepage_more_on_govuk.css
-//= link views/_homepage_more_on_govuk_new.css
+//= link_tree ../builds

app/assets/config/manifest.js

@@ -0,0 +1,24 @@
+app_stylesheets = {
+  "application.scss" => "application.css",
+  "components/_calendar.scss" => "components/_calendar.css",
+  "components/_metadata.scss" => "components/_metadata.css",
+  "components/_subscribe.scss" => "components/_subscribe.css",
+  "views/_calendars.scss" => "views/_calendars.css",
+  "views/_cookie-settings.scss" => "views/_cookie-settings.css",
+  "views/_csv_preview.scss" => "views/_csv_preview.css",
+  "views/_homepage_header.scss" => "views/_homepage_header.css",
+  "views/_homepage_more_on_govuk_new.scss" => "views/_homepage_more_on_govuk_new.css",
+  "views/_homepage_more_on_govuk.scss" => "views/_homepage_more_on_govuk.css",
+  "views/_homepage_new.scss" => "views/_homepage_new.css",
+  "views/_homepage.scss" => "views/_homepage.css",
+  "views/_inverse_header.scss" => "views/_inverse_header.css",
+  "views/_links_and_search.scss" => "views/_links_and_search.css",
+  "views/_local-transaction.scss" => "views/_local-transaction.css",
+  "views/_location_form.scss" => "views/_location_form.css",
+  "views/_popular_links.scss" => "views/_popular_links.css",
+  "views/_report-child-abuse.scss" => "views/_report-child-abuse.css",
+  "views/_travel-advice.scss" => "views/_travel-advice.css",
+}
+
+all_stylesheets = app_stylesheets.merge(GovukPublishingComponents::Config.all_assets)
+Rails.application.config.dartsass.builds = all_stylesheets