Migrate the Todos API to use `issuable_iid`

- Instead of `issuable_id`

lib/api/todos.rb

@@ -5,8 +5,8 @@ module API
     before { authenticate! }
 
     ISSUABLE_TYPES = {
-      'merge_requests' => ->(id) { find_merge_request_with_access(id) },
-      'issues' => ->(id) { find_project_issue(id) }
+      'merge_requests' => ->(iid) { find_merge_request_with_access(iid) },
+      'issues' => ->(iid) { find_project_issue(iid) }
     }.freeze
 
     params do
@@ -14,13 +14,13 @@ module API
     end
     resource :projects do
       ISSUABLE_TYPES.each do |type, finder|
-        type_id_str = "#{type.singularize}_id".to_sym
+        type_id_str = "#{type.singularize}_iid".to_sym
 
         desc 'Create a todo on an issuable' do
           success Entities::Todo
         end
         params do
-          requires type_id_str, type: Integer, desc: 'The ID of an issuable'
+          requires type_id_str, type: Integer, desc: 'The IID of an issuable'
         end
         post ":id/#{type}/:#{type_id_str}/todo" do
           issuable = instance_exec(params[type_id_str], &finder)

spec/requests/api/todos_spec.rb

@@ -163,7 +163,7 @@ describe API::Todos, api: true do
 
   shared_examples 'an issuable' do |issuable_type|
     it 'creates a todo on an issuable' do
-      post api("/projects/#{project_1.id}/#{issuable_type}/#{issuable.id}/todo", john_doe)
+      post api("/projects/#{project_1.id}/#{issuable_type}/#{issuable.iid}/todo", john_doe)
 
       expect(response.status).to eq(201)
       expect(json_response['project']).to be_a Hash
@@ -180,7 +180,7 @@ describe API::Todos, api: true do
     it 'returns 304 there already exist a todo on that issuable' do
       create(:todo, project: project_1, author: author_1, user: john_doe, target: issuable)
 
-      post api("/projects/#{project_1.id}/#{issuable_type}/#{issuable.id}/todo", john_doe)
+      post api("/projects/#{project_1.id}/#{issuable_type}/#{issuable.iid}/todo", john_doe)
 
       expect(response.status).to eq(304)
     end
@@ -195,7 +195,7 @@ describe API::Todos, api: true do
       guest = create(:user)
       project_1.team << [guest, :guest]
 
-      post api("/projects/#{project_1.id}/#{issuable_type}/#{issuable.id}/todo", guest)
+      post api("/projects/#{project_1.id}/#{issuable_type}/#{issuable.iid}/todo", guest)
 
       if issuable_type == 'merge_requests'
         expect(response).to have_http_status(403)