Add import/export feature for bookmarks (#14956)

* Add ability to export bookmarks

* Add support for importing bookmarks

* Add bookmark import tests

* Add bookmarks export test

spec/controllers/settings/exports/bookmarks_controller_specs.rb

@@ -0,0 +1,17 @@
+require 'rails_helper'
+
+describe Settings::Exports::BookmarksController do
+  render_views
+
+  describe 'GET #index' do
+    it 'returns a csv of the bookmarked toots' do
+      user = Fabricate(:user)
+      user.account.bookmarks.create!(status: Fabricate(:status, uri: 'https://foo.bar/statuses/1312'))
+
+      sign_in user, scope: :user
+      get :index, format: :csv
+
+      expect(response.body).to eq "https://foo.bar/statuses/1312\n"
+    end
+  end
+end