Flow2: Poll for auth result upon account setup wizard window activation

Flow2: Poll for auth result upon account setup wizard window activation

Since the default remote poll interval has been re-raised recently to 30 seconds,
the delay between clicking "Grant access" in the browser and fetch and showing success
in the wizard may seem erroneous to the users and tempt them to click "Re-open browser"
again, causing the whole login process to restart.

This commit implements an event handler to pass the wizard's window activation
event down to the Login Flow v2 page, in order to allow it to poll earlier.

Signed-off-by: Michael Schuster <michael@schuster.ms>