Allow bottom nav items to gain focus on keyboard traversal.

Set the bottom nav items to always be focusable. This addresses a bug in which bottom nav items didn't gain focus by keyboard pre-O.

PiperOrigin-RevId: 204518309

Author: afohrman

lib/java/com/google/android/material/bottomnavigation/BottomNavigationItemView.java

@@ -92,6 +92,7 @@ public BottomNavigationItemView(Context context, AttributeSet attrs, int defStyl
     // the content description of the BottomNavigationItemView should be used for accessibility.
     ViewCompat.setImportantForAccessibility(smallLabel, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_NO);
     ViewCompat.setImportantForAccessibility(largeLabel, ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_NO);
+    setFocusable(true);
     calculateTextScaleFactors(smallLabel.getTextSize(), largeLabel.getTextSize());
   }