[native] update FarcasterPrompt based on if the fid is set or not

Summary:
This diff updates the text content of FarcasterPrompt based on wheter or not the user is logged into farcaster or not (we determine this by whether or not the comm user has an fid set)

Depends on D11483

Test Plan:
Please see the screenshots below

When fid is set:

When fid is not set:

Confirmed that these changes to FarcasterPrompt do NOT affect the registration flow

Reviewers: atul, ashoat

Reviewed By: atul, ashoat

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11484