[WIP] Match TOTP modal to SMS/Voice modal

[cbhernan]

What does this PR do?

This PR makes the Authenticator modal look the same way as the SMS/Voice modal, which is smaller and extends to the necessary width, and full screen on smaller screens.

[codecov]

Codecov Report

Attention: Patch coverage is 84.89583% with 29 lines in your changes missing coverage. Please review.

Project coverage is 80.47%. Comparing base (bba3b6a) to head (538a41b).

Files with missing lines	Patch %	Lines
lib/views/dialogs/mobile.dart	80.76%	15 Missing ⚠️
lib/utils/BaseMFADialogState.dart	71.42%	8 Missing ⚠️
lib/views/dialogs/authenticator.dart	89.47%	6 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #133      +/-   ##
===============================================
+ Coverage        80.44%   80.47%   +0.02%     
===============================================
  Files               16       17       +1     
  Lines             1028     1019       -9     
===============================================
- Hits               827      820       -7     
+ Misses             201      199       -2     

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