Switch to secure random strings (#29013)

* Switch to secure random strings

Because the js-sdk methods are changing and there's no reason for these
not to use the secure versions. The dedicated upper/lower functions were
*only* used in this one case, so this should do the exact same thing with
the one exported function.

Requires https://github.com/matrix-org/matrix-js-sdk/pull/4621 (merge both together)

* Change remaining instances of randomString

which I somehow entirely missed the first time.

* Fix import order

test/unit-tests/components/views/spaces/SpaceSettingsVisibilityTab-test.tsx

@@ -8,7 +8,7 @@ Please see LICENSE files in the repository root for full details.
 
 import React from "react";
 import { mocked } from "jest-mock";
-import { randomString } from "matrix-js-sdk/src/randomstring";
+import { secureRandomString } from "matrix-js-sdk/src/randomstring";
 import { act, fireEvent, render, RenderResult } from "jest-matrix-react";
 import { EventType, MatrixClient, Room, GuestAccess, HistoryVisibility, JoinRule } from "matrix-js-sdk/src/matrix";
 
@@ -92,7 +92,7 @@ describe("<SpaceSettingsVisibilityTab />", () => {
 
     beforeEach(() => {
         let i = 0;
-        mocked(randomString).mockImplementation(() => {
+        mocked(secureRandomString).mockImplementation(() => {
             return "testid_" + i++;
         });