Treat the parent `UISearchBar` as the first responder when a `UISearchBarTextField` is the first responder.

This enables you to write natural test expectations against the `UISearchBar` accessibility label since the `UISearchBarTextField` instance is private and you cannot configure an accessibility label.
Merge pull request #250 from blakewatters/feature/UISearchBar-firstResponder

Treat parent `UISearchBar` as first responder when `UISearchBarTextField` instance is the first responder