Expose stable_id on champ

app/models/champ.rb

@@ -86,6 +86,10 @@ class Champ < ApplicationRecord
     true
   end
 
+  def stable_id
+    type_de_champ.stable_id
+  end
+
   private
 
   def needs_dossier_id?

app/models/champs/carte_champ.rb

@@ -74,7 +74,7 @@ class Champs::CarteChamp < Champ
   def to_feature_collection
     {
       type: 'FeatureCollection',
-      id: type_de_champ.stable_id,
+      id: stable_id,
       bbox: bounding_box,
       features: (legacy_selections_utilisateur + except_selections_utilisateur).map(&:to_feature)
     }

app/models/champs/repetition_champ.rb

@@ -35,7 +35,7 @@ class Champs::RepetitionChamp < Champ
 
   # We have to truncate the label here as spreadsheets have a (30 char) limit on length.
   def libelle_for_export
-    str = "(#{type_de_champ.stable_id}) #{libelle}"
+    str = "(#{stable_id}) #{libelle}"
     # /\*?[] are invalid Excel worksheet characters
     ActiveStorage::Filename.new(str.delete('[]*?')).sanitized.truncate(30)
   end

app/views/shared/dossiers/editable_champs/_carte.html.haml

@@ -10,4 +10,4 @@
   = render partial: 'shared/champs/carte/geo_areas', locals: { champ: champ, error: false }
 
 = form.hidden_field :value,
-  data: { remote: true, feature_collection_id: champ.type_de_champ.stable_id, url: champs_carte_path(form.index), params: champ_carte_params(champ).to_query, method: 'post' }
+  data: { remote: true, feature_collection_id: champ.stable_id, url: champs_carte_path(form.index), params: champ_carte_params(champ).to_query, method: 'post' }