[native] Introduce PasswordSelection screen

Summary:
This screen will be used for selecting a password for non-ETH accounts. Eventually we'll also allow ETH accounts to set a password.

This diff just sets up the scaffolding for the page. Later diffs will add functionality.

Test Plan:
Here's what it looks like now:

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7969