[Bug]: Contact names should not allow duplication

### Describe the bug:

When adding a new contact, there is no verification is the name collides with an existing contact, nor with existing local accounts:

### Expected behavior

Adding a new contact with the same name as an existing contact, or with one of the reserved account names should be disallowed, unless the address also matches.

### Screenshots/Recordings


### Steps to reproduce

1. go to `Settings / Contacts`
2. click `Add Contact`
3. use the name of an existing contact but a different address
4. observe that there is no error when you click `Save`
5. observe that 2 contacts appear in your address book with the same name

### Environment

Browser: Brave (but probably all)
Build type: production
Version: 12 (but the issue is older)