Improve the confirmation step of the "Add new bridges" dialog

Tor Browser 13.5 introduced a second, confirmation step to the "Add new bridges" dialog. At present it looks like this:

This confirmation step provides Tor Browser with the opportunity to fork the user journey between traditional and lox bridges (Alpha only), and provides space for basic error validation before presenting the Connect button.

However, other improvements could be made – e.g.:

• The current copy is terse, and doesn't explain the purpose of the confirmation step.
• Focus is applied to the first bridge in the list – this seems strange, and looks unusual.
• There is no back button to rectify a potential error. Users can only hit "Cancel" to start again.
• We could use this opportunity to introduce users to bridge-moji, and encourage them to check the emoji against their source (if applicable).

We could also implement the resulting design (or a version of it) at the end "Request bridges" flow too – however this should be spun off into a separate issue.