Cypress typescript (#13591)

* convert Cypress tests to TypeScript

this work was done by @lunaisnotaboy https://github.com/lunaisnotaboy
for their fork https://github.com/cutiekey/cutiekey/pull/7

I just repacked their changes into a minimal set

* fix call to `window` in cypress tests

this error was spotted thanks to the TypeScript compiler:

```
support/commands.ts:33:12 - error TS2559: Type '(win: any) => void'
has no properties in common with type 'Partial<Loggable &
Timeoutable>'.

33  cy.window(win => {
              ~~~~~~~~

Found 1 error in support/commands.ts:33
```

(again, @lunaisnotaboy did the actual work)

cypress/support/index.ts

@@ -0,0 +1,19 @@
+declare global {
+	namespace Cypress {
+		interface Chainable {
+			login(username: string, password: string): Chainable<void>;
+
+			registerUser(
+				username: string,
+				password: string,
+				isAdmin?: boolean
+			): Chainable<void>;
+
+			resetState(): Chainable<void>;
+
+			visitHome(): Chainable<void>;
+		}
+	}
+}
+
+export {}