Fix #3939: Add Screen Time support.

[iccub]

Summary of Changes

Old PR by our contributor here #7639

This pull request fixes #3939
Security review https://github.com/brave/reviews/issues/1383

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()
• New or updated UI has been tested across:
  • Light & dark mode
  • Different size classes (iPhone, landscape, iPad)
  • Different dynamic type sizes

Test Plan:

1. Verify that when you stay on a website for a bit it is tracked in Screen Time section in iOS settings.
2. Verify that after setting a time limit for a website, after you reach the limit you are not able to access it anymore.
3. Verify that websites are not tracked in private browsing mode

Disabled tests:

1. Turn off the feature - verify that websites are not tracked again
2. Turn off the feature - verify that the website where you reached the time limit can be accessed

Screenshots:

All the in-website UI is Apple controlled.

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • bug / enhancement
• Necessary security reviews have taken place.
• Adequate unit test coverage exists to prevent regressions.
• Adequate test plan exists for QA to validate (if applicable).
• Issue and pull request is assigned to a milestone (should happen at merge time).