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

res/css/views/dialogs/_InviteDialog.pcss

@@ -63,17 +63,6 @@ Please see LICENSE files in the repository root for full details.
         height: 25px;
         line-height: $font-25px;
     }
-
-    .mx_InviteDialog_buttonAndSpinner {
-        .mx_Spinner {
-            /* Width and height are required to trick the layout engine. */
-            width: 20px;
-            height: 20px;
-            margin-inline-start: 5px;
-            display: inline-block;
-            vertical-align: middle;
-        }
-    }
 }
 
 .mx_InviteDialog_section {
@@ -218,6 +207,10 @@ Please see LICENSE files in the repository root for full details.
     flex-direction: column;
     flex-grow: 1;
     overflow: hidden;
+
+    .mx_InviteProgressBody {
+        margin-top: var(--cpd-space-12x);
+    }
 }
 
 .mx_InviteDialog_transfer {

res/css/views/dialogs/_InviteProgressBody.pcss

@@ -0,0 +1,16 @@
+/*
+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.
+*/
+
+.mx_InviteProgressBody {
+    text-align: center;
+    font: var(--cpd-font-body-lg-regular);
+
+    h1 {
+        color: var(--cpd-color-text-primary);
+        font: var(--cpd-font-heading-sm-semibold);
+    }
+}