Parent #13326

This PR handles ignore threat action on the threat details screen.
Child PR for IgnoreThreatUseCase: #13767

It mimics behaviour on the web:

1. Displays a confirmation dialog
2. Disables buttons while action is taking place
3. Displays success/ error messages when action completes
4. Refreshes scan state when ignore threat action is successful

To test:
Prerequisite:

• Make sure both Scan feature flag and MySiteImprovements flag are set to on in the App settings.
• You have access to WP.com account with a site having scan capability and threats (e.g. https://pressable-jetpack-daily-scan.mystagingwebsite.com). Server credentials should be set on the site.
• I've added a threat to the site. In case you run out of threats, re-install bad calendar plugin from here and re-run scan.

1. Login to the app using above WP.com account and select the site on the My Site tab
2. Click scan menu item on My Site
3. Notice that scan state is fetched and shown with threats
4. Click a threat
5. Click ignore threat button on the threat details screen
6. Notice that a confirmation dialog is shown (see video)
7. Click ok in the confirmation dialog
8. Notice that action buttons are disabled
9. Wait for some time till ignore threat action completes
10. Notice that success message "Threat ignored." is shown
11. Notice that _update to scan state is triggered after ~2 secs

Repeat above steps and enable airplane mode after step 6. Notice that an error message is displayed and actions buttons are re-enabled.

(Tests included in ThreatDetailsViewModelTest )

Notes

1. Ignore all styling
2. Server credentials check is not handled
3. Loading state while action is taking place - yet to be added

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.