Refactor HomeFragment to be more testable

[sblatz]

Currently there is a lot of code in HomeFragment that cannot be tested because it needs to be abstracted out. Let's refactor this code out and write some tests for it 😄

┆Issue is synchronized with this Jira Task

[NotWoods]

Some suggestions:

• Move BrowserSessionsObserver to its own file.
• Uplift getting only normal/only private sessions to Android Components.
• Move the search engine icon (in the search bar) to its own custom view, or move the entire search bar.
  • Maybe Android Components should have a search bar with icon component.
• Move toolbarPaddingDp to dimens.xml.
• Move the private browsing button to a custom view
• Move preDrawListener to a custom class that implements LifecycleObserver.
• handleTabAction/handleCollectionAction should be moved somewhere else, maybe an interactor.