For #4495 - Clean up homescreen toolbar focus and content descriptions

[ekager]

• "Search or enter address" text is now centered correctly and doesn't jump around
• toolbar_wrapper takes the click listener so you can click anywhere on the toolbar (including over the search engine icon) and should navigate
• make search engine icon and toolbar text not focusable and not important for accessibility and give toolbar_wrapper the content description and focus
• Remove autofocusing of toolbar (This was discussed in When launching Fenix, Enable private browsing button is focused instead of Search or address #2142 so we forced focus but this caused other issues ([Bug][A11y] Private browsing is focused for a second at first launch #4447 and [Bug][a11y]Talkback jumps from reading the Tabs to search bar  #4489))
• Make Firefox Preview icon not focusable (app name is already read as you open it)

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or does not need one
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features

[colintheshots]

This looks good. Do we want "enable private browsing" to be the first item read on the home screen just because it's located at the top? We could use setTraversalBefore if the ordering seems wrong.

[ekager]

I think we want to remove any accessibility changes here for now because it was causing other issues and I'm not sure we should be changing the hierarchy here, but I will link that setTraversalBefore in the ticket as something to explore.