fix: blink while switching screens (#9705)

Fix to prevent showing blank screen while screens switching process.
Currently we can see it using dark background color in screens.
This fix also makes clear work with eager loading of screens (`detachInactiveScreens={false}` `lazy={false}`).

packages/drawer/src/views/DrawerView.tsx

@@ -225,7 +225,7 @@ function DrawerViewBase({
           return (
             <MaybeScreen
               key={route.key}
-              style={[StyleSheet.absoluteFill, { opacity: isFocused ? 1 : 0 }]}
+              style={[StyleSheet.absoluteFill, { zIndex: isFocused ? 0 : -1 }]}
               visible={isFocused}
               enabled={detachInactiveScreens}
             >