Add Autocomplete pixels

[ayoy]

Task/Issue URL: https://app.asana.com/0/1177771139624306/1207226295114884/f

Description:
This change adds a bunch of pixels related to selecting suggestions in the address bar.

Steps to test this PR:

1. Go to Settings -> General
2. Toggle autocomplete checkbox. Verify that it emits m_mac_autocomplete_toggled_on and m_mac_autocomplete_toggled_off as expected.
3. Add 2 bookmarks, mark one of them as favorite.
4. Keep autocomplete selected.
5. Type a phrase in the address bar and click on a search phrase suggestion. Verify that it emits m_mac_autocomplete_click_phrase.
6. Type a website address in the address bar and click on a website suggestion. Verify that it emits m_mac_autocomplete_click_website.
7. Type the bookmark name and click on a bookmark suggestion. Verify that it emits m_mac_autocomplete_click_bookmark.
8. Type the favorite name and click on a bookmark suggestion. Verify that it emits m_mac_autocomplete_click_favorite.
9. Type part of the address/title of a website you've visited previously. Click on a history suggestion. Verify that it emits m_mac_autocomplete_click_history.
10. Verify that 5-9 also work for selecting the suggestion using keyboard (navigating with keys and pressing Enter).

---

Internal references:

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

[SabrinaTardio]

LGTM!