Update examples to TypeScript.

It seems to be impossible to write straightforward code with JSDoc annotations that is correctly typed in both JS and TS files, because the `@type` annotations are not correctly applied to the dynamic import. So we just provide a straight-up TypeScript example, and folks can remove the types if they are using JS.

Author: lgarron

README.md

@@ -14,25 +14,29 @@ By design, these are compatible with `@github/webauthn-json` encoding, so you ca
 
 If you need to support older browsers in the short-term, consider loading this library only as a fallback:
 
-```js
+```ts
+// Example in TypeScript
+
 async function register() {
   const parseCreationOptionsFromJSON =
     PublicKeyCredential.parseCreationOptionsFromJSON ??
-      /* @type PublicKeyCredential.parseCreationOptionsFromJSON */
-      (await import("@github/webauthn-json/browser-ponyfill")).parseCreationOptionsFromJSON;
+      ((await import("@github/webauthn-json/browser-ponyfill"))
+        .parseCreationOptionsFromJSON as unknown as typeof PublicKeyCredential.parseCreationOptionsFromJSON);
 
   const publicKey = parseCreationOptionsFromJSON({ /* … */ });
-  return navigator.credentials.create({publicKey});
+  const credential = (await navigator.credentials.create({publicKey})) as PublicKeyCredential;
+  return credential.toJSON();
 }
 
 async function authenticate() {
   const parseRequestOptionsFromJSON =
     PublicKeyCredential.parseRequestOptionsFromJSON ??
-      /* @type PublicKeyCredential.parseRequestOptionsFromJSON */
-      (await import("@github/webauthn-json/browser-ponyfill")).parseRequestOptionsFromJSON;
+      ((await import("@github/webauthn-json/browser-ponyfill"))
+        .parseRequestOptionsFromJSON as unknown as typeof PublicKeyCredential.parseRequestOptionsFromJSON);
 
   const publicKey = parseRequestOptionsFromJSON({ /* … */ });
-  return navigator.credentials.get({publicKey});
+  const credential = (await navigator.credentials.get({publicKey})) as PublicKeyCredential;
+  return credential.toJSON();
 }
 ```