Update email settings UI and handle account reunification

[artemruts]

Description

To support account reunification when we have multiple "Continue with {codehost}" options,
we need to provide better support for verifying and setting primary email addresses.
This in turn will help us make sure users can't have two separate accounts for different code hosts.

Acceptance Criteria

• Update current "Emails" view
• Design updates to list of emails
• Remove "Mark as unverified" action
• Add "Primary email address" (Disabled unless the user has more than one verified email) - depends on User can set primary email #15393
• Enable account unification - depends on #TODO

When user signs in with code host not already associated with an account,
check the returned email address against verified emails in existing accounts.
If the account matches, reunify the account.

Account reunification inherently creates a new code host connection.

Resources

• ✨ Figma
• 📃 Productboard

[github-actions]

Heads up @tsenart - the "team/cloud" label was applied to this issue.

[tsenart]

@ryanslade: Is the account reunification part of this already done?