#6068238 Support removing email forwards from the email plan page

Changes proposed in this Pull Request

This PR makes the following changes:

• The existing ActionMenu function and its helpers has been refactored into a new EmailMailboxActionMenu component (with some minor modifications to the arguments and code structure)
• The PopoverMenuItem now has documentation for its onClick prop and a note that external links require an href prop to be accessible
• We now have a new “Remove email forward” menu item for email forwards
• We have removed the existing “Edit” menu item for email forwards — the only action for forwards other than removing a forward or resending the verification email is to create a new forward, and that’s not a mailbox-specific action.
• The main EmailPlan component has the existing email forward state wired in so we can detect when updates occur and we need to refetch the email data for the current domain
  • The current implementation here is not ideal as we’re bridging the email forwarding state changes across to the new email provider API, but we don’t have that data cleanly handled via Redux yet, so we’ll need to take that on separately

Testing instructions

• Run this branch locally or via the live branch.
• Set up two email forwards for a domain you own. (This is currently performed outside the email plan page.)
• Navigate to the email plan page for your domain with email forwards.
• Open your browser network tab.
• For one of the email forwards, open the action/kebab menu for the email.
• Verify that the only option in the menu is “Remove email forward”.
• Click on the “Remove email forward” option.
• Verify that we triggered a calypso_email_management_email_forwarding_delete_click Tracks event.
• Verify that you see a success notice appear.
• Verify that the page is updated and no longer shows the removed email forward.
• Click on the “Remove email forward” menu item for the last email forward.
• Verify that we remove the forward as above and show the email plan page with “No mailboxes”

Screenshot