Use numeric input control for TOTP factor entry

Summary:
Finishes fixing T11365. rP28199bcb48 added the new numeric entry
control and used it for TOTP setup, but missed the case of entering
a factor when TOTP was already set up.

Test Plan:
Observe behaviour of TOTP setup and subsequent factor entry
in iOS browser, make sure they're consistent.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley

Maniphest Tasks: T11365

Differential Revision: https://secure.phabricator.com/D16325