[landing/lib/native] introduce FarcasterWebView

Summary:
This component will be used to talk to BASE_LANDING_URL/connect-farcaster route that was just introduced prior in this stack. Based on the FarcasterWebViewMessage type this webview will either redirect the user to the farcaster app if they have it, safari with a link to download the app if they don't have farcaster, or return the user's fid to the onSuccess callback if the farcaster user data is returned back to the webview

Also in this diff I snuck in factoring out some shared types into their own file rather than copying + pasting the same type across different files

Depends on D11429

Test Plan: Tested the entire sign in flow during the hackathon

Reviewers: atul

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11432