Fix #1941: Add App Store scheme handling for new App Store redirects

[kylehickinson]

Also make sure snack bar alerts show above new tab overlay

Note: Snackbar UI is currently broken (possible regression of #1736), but otherwise works

Summary of Changes

This pull request fixes issue #1941

Submitter Checklist:

• Unit Tests are updated to cover new or changed functionality
• User-facing strings use NSLocalizableString()

Test Plan:

Additional test plan other than what's found in issue:

• Open an empty new tab
• Paste https://apps.apple.com/us/app/brave-fast-privacy-web-browser/id1052879175 into the URL bar and go
• Verify that the "Open in App Store" snack bar alert thing shows up at the bottom of the tab

Reviewer Checklist:

• Issues include necessary QA labels:
  • QA/(Yes|No)
  • release-notes/(include|exclude)
  • 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 is assigned to a milestone (should happen at merge time).