Cypress: skip tests known to fail when using Rust crypto (#10873)

* Cypress: skip tests known to fail when using Rust crypto

... which means we can then run the cypress test suite against Element Web R to
check we aren't introducing regressions.

* Update cypress/e2e/register/register.spec.ts

* Use env var to detect rust crypto

* Hoist `skipIfRustCrypto` call earlier

cypress/support/config.json.ts

@@ -20,6 +20,8 @@ limitations under the License.
  * we make requests to the live `matrix.org`, which makes our tests dependent on matrix.org being up and responsive.
  */
 
+import { isRustCryptoEnabled } from "./util";
+
 const CONFIG_JSON = {
     // This is deliberately quite a minimal config.json, so that we can test that the default settings
     // actually work.
@@ -40,7 +42,7 @@ beforeEach(() => {
     const configJson = CONFIG_JSON;
 
     // configure element to use rust crypto if the env var tells us so
-    if (Cypress.env("RUST_CRYPTO")) {
+    if (isRustCryptoEnabled()) {
         configJson["features"] = {
             feature_rust_crypto: true,
         };

cypress/support/util.ts

@@ -56,5 +56,20 @@ cy.all = function all(commands): Cypress.Chainable {
     return cy.wrap(resultArray, { log: false });
 };
 
-// Needed to make this file a module
-export {};
+/**
+ * Check if Cypress has been configured to enable rust crypto, and bail out if so.
+ */
+export function skipIfRustCrypto() {
+    if (isRustCryptoEnabled()) {
+        cy.log("Skipping due to rust crypto");
+        //@ts-ignore: 'state' is a secret internal command
+        cy.state("runnable").skip();
+    }
+}
+
+/**
+ * Determine if Cypress has been configured to enable rust crypto (by checking the environment variable)
+ */
+export function isRustCryptoEnabled(): boolean {
+    return !!Cypress.env("RUST_CRYPTO");
+}