Add Search Bar on the New Tab Page

[ayoy]

Task/Issue URL: https://app.asana.com/0/72649045549333/1208262951113965/f

Description:
This change introduces alternative New Tab Page UI including a search bar.
The new UI exists alongside the original UI and will be enabled to some users as an experiment.
The NTP search bar reuses existing AddressBarTextField wrapped in an NSViewRepresentable.
There's AddressBarViewModel class created for interacting with SwiftUI views - it encapsulates
AddressBarViewController and forwards actions to it.
NTP content with search bar is now centered vertically in the view if all NTP sections are hidden
or in collapsed state.
This code is meant to be temporary and will be removed after the experiment finishes.

Steps to test this PR:

1. Run the app
2. Set internal user state
3. Close the window and reopen, verify that the New Tab Page contains a search bar.
4. Verify that the search bar works – typing queries, navigating to urls, opening search suggestions. Verify that cmd+return opens the query in a new tab.
5. Type text in search bar so that the suggestions window is displayed. Scroll NTP and verify that suggestions window disappears.
6. Shrink the window vertically and verify that it displays a more compact Dax logo.
7. Focus the search bar and scroll NTP so that the search bar is not visible. Start typing and verify that NTP scrolls down to reveal the search bar.
8. Click Customize button in the bottom-right corner of the NTP and hide all NTP sections. Verify that the search bar is (roughly) centered vertically inside the view.
9. Show Recently Visited section and collapse it. Verify that NTP content is centered vertically. Expand Recently Visited and verify that NTP content is not centered anymore.
10. Remove internal user state, close the window and reopen and verify that the search bar is not visible.

Definition of Done:

• Does this PR satisfy our Definition of Done?

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Internal references:

Pull Request Review Checklist
Software Engineering Expectations
Technical Design Template
Pull Request Documentation

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

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