Refactor CreateCrossSigningDialog (#28218)

* Refactor CreateCrossSigningDialog

 * Converts CreateCrossSigningDialog to a functional component
 * Pulls logic out to its own class
 * Updates usage of deprecated cross signing bootstrap method on client to be on the crypto object and updates test to match

Moved from https://github.com/element-hq/matrix-react-sdk/pull/131

* Add mock here too

* Use the right mock

* Remove duplicate mock

* Stray jest mock line

* Un-move mocks

* tsdoc

* Typo

Co-authored-by: Andy Balaam <andy.balaam@matrix.org>

---------

Co-authored-by: Andy Balaam <andy.balaam@matrix.org>

test/test-utils/test-utils.ts

@@ -125,6 +125,7 @@ export function createTestClient(): MatrixClient {
             getVerificationRequestsToDeviceInProgress: jest.fn().mockReturnValue([]),
             setDeviceIsolationMode: jest.fn(),
             prepareToEncrypt: jest.fn(),
+            bootstrapCrossSigning: jest.fn(),
             getActiveSessionBackupVersion: jest.fn().mockResolvedValue(null),
         }),