DEV: convert change owner modal to glimmer component (#23668)

* DEV: convert change owner modal to glimmer component

* DEV: add system test for change owner modal

spec/system/change_owner_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+describe "Change Owner Modal", type: :system do
+  fab!(:post) { Fabricate(:post, raw: "This is some post to change owner for") }
+  fab!(:other_user) { Fabricate(:user) }
+  fab!(:admin) { Fabricate(:admin) }
+  let(:user) { post.user }
+  let(:topic) { post.topic }
+  let(:topic_page) { PageObjects::Pages::Topic.new }
+  let(:change_owner_modal) { PageObjects::Modals::ChangeOwner.new }
+
+  before { sign_in(admin) }
+
+  def visit_topic_and_open_change_owner_modal(post)
+    topic_page.visit_topic(topic)
+    topic_page.expand_post_actions(post)
+    topic_page.expand_post_admin_actions(post)
+    topic_page.click_post_admin_action_button(post, :change_owner)
+  end
+
+  it "changes owner of a post" do
+    visit_topic_and_open_change_owner_modal(post)
+    change_owner_modal.select_new_owner(other_user)
+    change_owner_modal.confirm_new_owner
+    expect(page).not_to have_css ".change-ownership-modal"
+
+    displayed_username = topic_page.post_by_number(post).find(".first.username").text
+    expect(displayed_username).to eq other_user.username
+  end
+end