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/unit-tests/components/structures/MatrixChat-test.tsx

@@ -1112,8 +1112,6 @@ describe("<MatrixChat />", () => {
 
                 expect(loginClient.getCrypto()!.userHasCrossSigningKeys).toHaveBeenCalled();
 
-                await flushPromises();
-
                 // set up keys screen is rendered
                 expect(screen.getByText("Setting up keys")).toBeInTheDocument();
             });