Update the UI of the login flow

[planarvoid]

The task is to update the UI of all the steps of the login/signup flow. This flow uses shared components so the screen changes will be overlapping

• The toolbar is changing, instead of a logo it now contains a title with the flow you're in ("Get Started" changes either into "Log In" or into "Sign Up"), the help is now an icon
• The action buttons are moving to the bottom of the screen
• The colors and styling are changing
• Go step by step and compare the screens to the desings to see all the changes
• If possible, the changes should be behind a feature flag

[renanferrari]

This issue will be handled by multiple PRs:

• Updates to the Login Library theme and styles: Unified Login & Sign-Up: Login library theme and styles update #12047
• Updates to the Login Library existing screens layouts: Unified Login & Sign-Up: Login library screen layouts update #12048
  • Login Email Screen
  • Login Email Password Screen
  • Login Magic Link Request Screen
  • Login Magic Link Sent Screen
  • Login 2FA Screen
  • Login Site Address Screen
  • Login Username Password Screen
  • Signup Email Screen
  • Signup Magic Link Screen
• Addition of the new Signup Confirmation screen to the new Login library: Unified Login & Sign-Up: Add Signup Confirmation screen #12056