Add WebAuthn and Magic Links in auth-nextjs

[scotttrinh]

EdgeDB 5.0 adds two new passwordless authentication mechanisms: WebAuthn and Magic Links.

• WebAuthn doesn't support a Server Actions flow since it is a back-and-forth ceremony via JSON that makes some client-side calls, so webauthn methods are exported as a separate module. This necessitated breaking the app router into server and client parts as well, but I left the "server" export as index.ts. Should I update that? Alias it?
• The documentation needs a pretty big overhaul to cover how you would set up each different authentication flow, but that feels out of scope for this PR. Will add as part of the 5.0 effort.
• Terminology is a little muddled in the Magic Link flow: sign-in vs send being the most obvious one. I'd like to get some feedback here and update to be consistent: What should the action that sends an email to an already registered Magic Link factor be named? Feels like "send" is more correct, but is that confusing?