Update MultiInviter to take an options object (#30541)

* Move `inviteUsersToRoom` to `RoomUpgrade`

This method is only used in one place, uses only public methods, and is
undocumented. Let's move it to the place where it is used, to simplify the API
for `RoomInvite`.

* Simplify `inviteUsersToRoom`

`inviteMultipleToRoom` basically never throws, so this code was effectively
unreachable.

* Update MultiInviter to take an options object

I'm going to add another option, so an options object is going to be more
flexible.

* Jump through the coverage hoop with another test

test/unit-tests/RoomInvite-test.ts

@@ -0,0 +1,33 @@
+/*
+Copyright 2025 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.
+*/
+
+import { getMockClientWithEventEmitter } from "../test-utils";
+import { inviteMultipleToRoom } from "../../src/RoomInvite.tsx";
+
+afterEach(() => {
+    jest.restoreAllMocks();
+});
+
+describe("inviteMultipleToRoom", () => {
+    it("can be called wth no `options`", async () => {
+        const client = getMockClientWithEventEmitter({});
+        const { states, inviter } = await inviteMultipleToRoom(client, "!room:id", []);
+        expect(states).toEqual({});
+
+        // @ts-ignore reference to private property
+        expect(inviter.options).toEqual({});
+    });
+});