Show a "progress" dialog while invites are being sent (#30561)

* InviteDialog: show some words and a spinner while invites are being sent

* MultiInviter-test: avoid building unhandled rejected promises

If we don't handle rejected promises, jest gets confused by them. Instead,
let's create them on-demand.

* Open a "progress" dialog while invites are being sent

* Inhibit invite progress dialog when RoomUpgradeWarning dialog is kept open

... otherwise the `RoomUpgradeWarning` dialog disappears during the invites,
and the tests that assert that it is showing the correct thing fail.
 enter the commit message for your changes. Lines starting

* Switch to compound CSS variables instead of old pcss vars

* update playwright screenshots

* Revert "update playwright screenshots"

This reverts commit b0a15d97f35a088fe5b67009085eab46be1316fd.

* Another go at updating screenshots

* Address review comments

* remove redundant Props

test/unit-tests/components/views/dialogs/InviteProgressBody-test.tsx

@@ -0,0 +1,18 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import React from "react";
+import { render } from "jest-matrix-react";
+
+import InviteProgressBody from "../../../../../src/components/views/dialogs/InviteProgressBody.tsx";
+
+describe("InviteProgressBody", () => {
+    it("should match snapshot", () => {
+        const { asFragment } = render(<InviteProgressBody />);
+        expect(asFragment()).toMatchSnapshot();
+    });
+});