Cypress test for incoming verification requests (#11123)

* Cypress: move verification tests to their own file

* Remove redundant cypress test

This does nothing that the verification test doesn't do better.

* Factor `beginKeyVerification` call out of `doTwoWaySasVerification`

... for more flexibility. This allows us to have tests where the other side
picks the verification method.

* Cypress test for incoming verification requests

cypress/support/toasts.ts

@@ -0,0 +1,27 @@
+/*
+Copyright 2023 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+/// <reference types="cypress" />
+
+/**
+ * Assert that a toast with the given title exists, and return it
+ *
+ * @param expectedTitle - Expected title of the test
+ * @returns a Chainable for the DOM element of the toast
+ */
+export function getToast(expectedTitle: string): Cypress.Chainable<JQuery> {
+    return cy.contains(".mx_Toast_toast h2", expectedTitle).should("exist").closest(".mx_Toast_toast");
+}