[FR][Phone Auth] Add capability to auto-proceed after user enters last digit of SMS code

[willbattel]

Currently, when authenticating with a phone number, the received text containing the code often times displays as a notification banner at the top of the screen, which hides the "Next" button in the navigation bar for several seconds unless swiped away. This probably doesn't outright churn a lot of our users but it definitely adds friction to the sign up/in process.

Because the codes are always the same length (at least, they have been thus far), I propose an option where, upon entering the last character of the code (also achievable by pressing the auto-complete suggestion on the keyboard), FUI automatically tries to proceed as if they had tapped "Next".

This pattern is fairly common, and removes one extra tap that probably isn't necessary. There may be technical challenges associated with implementing this but I wanted to put it on the floor for discussion.

[willbattel]

Took a screenshot showing how the text notification covers the Next button, requiring the user to either wait a few seconds for the notification to disappear or swiping the notification away. Neither option is ideal, especially considering the fact that the user often doesn't realize where the Next button is before receiving the notification, leading to momentary confusion on how to proceed.

[willbattel]

Another option would be to move the Next button to (or add another one) below the "Resend code" label and above the keyboard. I'd still prefer the auto-proceed on code completion but this would at least reduce confusion.

[willbattel]

This is still an annoying flaw...