tab manager multi select mode

[brindy]

Task/Issue URL: https://app.asana.com/0/392891325557410/1208685664909478/f
Tech Design URL:
CC:

Description:
Adds ability to multi-select tabs.

Refactored SwiftUI top bar view to use a transparent Navigation Bar (which wasn't available when we first built this screen)

Steps to test this PR:

1. Disable internal user
2. Open a few tabs and browse to some web pages
3. Smoke test previous behaviour remains the same (you can also run the bookmarks and bookmarks-multi UI tests)
4. Enable internal user
5. Validate UI vs Figma (iPhone and iPad)
6. Click edit and chose "Select tabs" to get into selection mode
7. Close all tabs from this menu should work
8. Once in this mode selecting and closing selected tabs should work
9. The menu in the circle with ellipsis is still WIP
10. Long press on the tabs doesn't do anything yet (other than allow re-ordering)
11. Validate UI on iOS 15

[github-actions]

	Fails
🚫	Please, make sure this PR satisfies our Definition of Done and the relevant checkbox is checked.

	Warnings
⚠️	PR has more than 500 lines of code changing. Consider splitting into smaller PRs if possible.

Generated by 🚫 dangerJS against eacff65

[brindy]

Going to re-open with more changes.