Move mail css back to be managed by wepack

It wil allow us to remove dependency on `rails-sass`, and `sass` which
are not maintained anymore.
More or less revert this PR: https://github.com/openfoodfoundation/openfoodnetwork/pull/12743

app/assets/stylesheets/mail.scss

@@ -1 +0,0 @@
-@import './mail/all.scss';

app/assets/stylesheets/mail/all.scss

@@ -1,3 +0,0 @@
-@import '../../../webpacker/css/admin/globals/palette.scss';
-@import 'email';
-@import 'payments_list';

app/helpers/application_helper.rb

@@ -76,4 +76,19 @@ module ApplicationHelper
   def cache_key_with_locale(key, locale)
     Array.wrap(key) + ["v2", locale.to_s, I18nDigests.for_locale(locale)]
   end
+
+  def pdf_stylesheet_pack_tag(source)
+    # With shakapacker dev server running, the wicked_pdf_stylesheet_pack_tag will produce a
+    # relative path, because we don't have `config.action_controller.asset_host`. Relative path
+    # can't be resolved by `wkhtmltopdf`. So we pass the wepacker dev server host and port to
+    # the shakapacker helper, so it generates the correct url.
+    # For more info: https://stackoverflow.com/questions/58490299/how-to-include-css-stylesheet-into-wicked-pdf/60541688#60541688
+    if running_in_development?
+      options = { media: "all",
+                  host: "#{Shakapacker.dev_server.host}:#{Shakapacker.dev_server.port}" }
+      stylesheet_pack_tag(source, **options)
+    else
+      wicked_pdf_stylesheet_pack_tag(source)
+    end
+  end
 end

app/views/layouts/mailer.html.haml

@@ -5,7 +5,7 @@
     %meta{:content => "text/html; charset=UTF-8", "http-equiv" => "Content-Type"}/
     %title
       = Spree::Config[:site_name]
-    = stylesheet_link_tag 'mail', media: "screen"
+    = stylesheet_pack_tag "mail", media: "screen"
   %body{:bgcolor => "#FFFFFF" }
     - unless @hide_ofn_navigation
       %table.head-wrap

app/views/spree/admin/orders/invoice.html.haml

@@ -1,4 +1,4 @@
-= wicked_pdf_stylesheet_link_tag "mail"
+= pdf_stylesheet_pack_tag "mail"
 
 %table{:width => "100%"}
   %tbody

app/views/spree/admin/orders/invoice2.html.haml

@@ -1,4 +1,4 @@
-= wicked_pdf_stylesheet_link_tag "mail"
+= pdf_stylesheet_pack_tag "mail"
 
 %table{:width => "100%"}
   %tbody

app/views/spree/admin/orders/invoice4.html.haml

@@ -1,4 +1,4 @@
-= wicked_pdf_stylesheet_link_tag "mail"
+= pdf_stylesheet_pack_tag "mail"
 
 %table{:width => "100%"}
   %tbody
@@ -102,4 +102,4 @@
   = render partial: 'spree/admin/orders/_invoice/order_note'
 
 .text-center
-  = link_to_platform_terms
+  = link_to_platform_terms

app/webpacker/css/mail/all.scss

@@ -0,0 +1,3 @@
+@import '../admin/globals/palette.scss';
+@import 'email';
+@import 'payments_list';

app/webpacker/packs/mail.scss

@@ -0,0 +1 @@
+@import "../css/mail/all.scss";

config/initializers/assets.rb

@@ -19,6 +19,5 @@ Rails.application.config.assets.precompile += [
   'web/all.js',
   'darkswarm/all.js',
   'shared/*',
-  'mail.scss',
   '*.jpg', '*.jpeg', '*.png', '*.gif' '*.svg',
 ]