[native] Introduce PasswordSelection screen
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.
Here's what it looks like now:
Reviewers: atul, ginsu
Reviewed By: atul
Differential Revision: https://phab.comm.dev/D7969