🪟 🔧 Cleaner error handling for authService's sendVerificationEmail

[ambirdsall]

What

When I first extracted this error handling code from EmailVerificationHint.tsx in #21623 so the enrollment modal could take advantage of it too, I missed a basic structural fix (because the internal API defined in authService had an identical type signature as the upstream firebase/auth function it wrapped, it Seemed Obvious:tm: that it was appropriate to port its error-handling code unchanged). To wit: because it handled errors within the Promise, rather than via the Promise, success/error code paths were being defined in different scopes; the only way to invalidate a downstream .then which should only run on success was to reraise the error. This lead to arbitrary and ugly .catch()es getting tacked onto both usage sites just to avoid crashing the page from an already-handled error.

But, like: that's the whole reason Promise.prototype.catch exists, though.

Testing

Manually tested via the enrollment modal, behaves exactly as before in both error and success states.

[josephkmh]

Thanks for refactoring this! Explanation makes sense, and this is much cleaner 👍