Fix #7996: Switching Private Mode Tab Tray cause position loss in Normal Mode

[soner-yuksel]

Summary of Changes

This pull request fixes #7996

Fixing normal mode private mode persistent tab switches as well as positioning in tab tray

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:

• Open Tab Tray
• Check which tab is highlighted in the collection view and where is the scrool
• Switch to private mode
• And back to normal mode
• Check position in Tab tray is lost entirely and positioned to top
• Check

Screenshots:

RPReplay_Final1693595151.mov

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).