Username and email display behavior

[0x4f53]

♻️ Current situation

The existing "Email as username" behavior is confusing. Time to fix that.

💡 Proposed solution

- Check for "Email as username" state. If checked, set username field to "null" upon item save only (prevents accidental erasure).

• Remove the "Email as username" switch to:
  a. Achieve parity with Keyspace browser plugin(s).
  b. Simplify the process of adding a login by preventing unnecessary and confusing options.
• If both email and username are set, prioritize username (helps with sites like reddit).

📋 Release Notes

• Changed username-email behavior to prioritize usernames in UI if set.
• Removed the "Email as username" switch

Testing

• Create a login with username and email and save it and observe the login card: the username is shown in the dashboard card but they're both displayed in the mini login dialog.
• Create a login with an username only and save it. Only the username is shown in both the login card and the mini dialog.
• Create a login with an email only and save it. Only the email is shown in both the login card and the mini dialog.
• Create a login with a name only and save it. Neither the email nor the username is shown in both the login card and the mini dialog.
  - Edit the login, check the "Email as username" switch, save it and observe again.