[fenix] For https://github.com/mozilla-mobile/fenix/issues/16238 - Back button now dismisses Suggested Logins

By using PromptFeature's onBackPressed the user can now press back to dismiss the Suggested Logins prompt without inadvertently navigating back

app/src/main/java/org/mozilla/fenix/browser/BaseBrowserFragment.kt

@@ -969,6 +969,7 @@ abstract class BaseBrowserFragment : Fragment(), UserInteractionHandler,
     override fun onBackPressed(): Boolean {
         return findInPageIntegration.onBackPressed() ||
                 fullScreenFeature.onBackPressed() ||
+                promptsFeature.onBackPressed() ||
                 sessionFeature.onBackPressed() ||
                 removeSessionIfNeeded()
     }