Inline the attachment form for taxon icons

There's no explicit support for multiple taxon attachment anywhere
else in the solidus codebase, and the attachment_partial_name was
using "paperclip" even for active_storage.

backend/app/views/spree/admin/taxons/_form.html.erb

@@ -20,7 +20,24 @@
       </div>
     <% end %>
 
-    <%= render "spree/admin/taxons/attachment_forms/#{f.object.attachment_partial_name}", f: f %>
+    <% if Spree::Config.keep_legacy_backend_support_for_multiple_taxon_attachments %>
+      <%= render "spree/admin/taxons/attachment_forms/#{f.object.attachment_partial_name}", f: f %>
+    <% else %>
+      <%= f.field_container :icon do %>
+        <%= f.label :icon %><br>
+        <%= f.file_field :icon %>
+        <% if f.object.icon_present? %>
+          <%= image_tag f.object.icon(:mini) %>
+          <%= link_to t('spree.actions.remove'),
+                      admin_taxonomy_taxon_attachment_path(@taxonomy,
+                                                           @taxon.id,
+                                                           attachment_definition: :icon,
+                                                           authenticity_token: form_authenticity_token),
+                      method: :delete,
+                      class: 'btn btn-sm btn-danger' %>
+        <% end %>
+      <% end %>
+    <% end %>
   </div>
 
   <div class="col-5">

backend/app/views/spree/admin/taxons/attachment_forms/_paperclip.html.erb

@@ -1,3 +1,11 @@
+<%
+Spree::Deprecation.warn(
+  "This partial with its support for multiple Spree::Taxon attachments is deprecated and will be removed in a future " \
+  "version of Solidus, please set Spree::Config.keep_legacy_backend_support_for_multiple_taxon_attachments to false " \
+  "and overwrite the standard view if you need to support custom attachments."
+)
+%>
+
 <% f.object.class.attachment_definitions.each do |attachment, definition| %>
   <%= f.field_container attachment do %>
     <%= f.label attachment %><br>

core/app/models/spree/taxon/active_storage_attachment.rb

@@ -9,11 +9,10 @@ module Spree::Taxon::ActiveStorageAttachment
                    styles: { mini: '32x32>', normal: '128x128>' },
                    default_style: :mini
     validate :icon_is_an_image
-
-
   end
 
   def attachment_partial_name
+    Spree::Deprecation.warn("calling #attachment_partial_name on Spree::Taxon is deprecated without replacement.")
     'paperclip'
   end
 end

core/app/models/spree/taxon/paperclip_attachment.rb

@@ -20,6 +20,7 @@ def icon_present?
   end
 
   def attachment_partial_name
+    Spree::Deprecation.warn("calling #attachment_partial_name on Spree::Taxon is deprecated without replacement.")
     'paperclip'
   end
 

core/lib/generators/solidus/install/templates/config/initializers/spree.rb.tt

@@ -22,7 +22,11 @@ Spree.config do |config|
   config.image_attachment_module = 'Spree::Image::ActiveStorageAttachment'
   config.taxon_attachment_module = 'Spree::Taxon::ActiveStorageAttachment'
 
-  # Defaults
+  # Defaults:
+
+  # Do not try to support custom paperclip attachments of Spree::Taxon.
+  config.keep_legacy_backend_support_for_multiple_taxon_attachments = false
+
   # Permission Sets:
 
   # Uncomment and customize the following line to add custom permission sets

core/lib/spree/app_configuration.rb

@@ -157,6 +157,11 @@ class AppConfiguration < Preferences::Configuration
     #   @return [Integer]
     preference :inventory_cache_threshold, :integer
 
+    # @!attribute [rw] keep_legacy_backend_support_for_multiple_taxon_attachments
+    #   @return [Boolean] should we keep the legacy HTML that will show a form for each paperclip attachment
+    #      defined on Spree::Taxon.
+    preference :keep_legacy_backend_support_for_multiple_taxon_attachments, :boolean, default: true
+
     # @!attribute [rw] layout
     #   @return [String] template to use for layout on the frontend (default: +"spree/layouts/spree_application"+)
     preference :layout, :string, default: 'spree/layouts/spree_application'