Handle undefined `PublicKeyCredential` in `browserSupportsWebAuthnAutofill` helper

Describe the issue

Currently, calling the browserSupportsWebAuthnAutofill helper on a browser without webauthn support will cause an error since it is trying to evaluate isConditionalMediationAvailable of undefined.

The helper should check whether PublicKeyCredential is defined first and resolve false if it isn't, similar to the platformAuthenticatorIsAvailable helper.

Code Samples + WebAuthn Options and Responses

import {
  browserSupportsWebAuthn,
  browserSupportsWebAuthnAutofill,
  platformAuthenticatorIsAvailable,
} from "@simplewebauthn/browser";

export const getPasskeySupportInfo = async () => {
  const hasWebAuthnSupport = browserSupportsWebAuthn();
  const hasWebAuthnAutofillSupport = await browserSupportsWebAuthnAutofill();
  const hasPlatformAuthenticator = await platformAuthenticatorIsAvailable();

  return {
    hasWebAuthnSupport,
    hasWebAuthnAutofillSupport,
    hasPlatformAuthenticator,
  };
};

Error message:

iOS: undefined is not an object (evaluating 'e.isConditionalMediationAvailable') Android: Cannot read properties of undefined (reading 'isConditionalMediationAvailable')

SimpleWebAuthn Libraries

$ npm list --depth=0 | grep @simplewebauthn
├── @simplewebauthn/browser@9.0.1
├── @simplewebauthn/types@9.0.1
# ...

MasterKale / SimpleWebAuthn