[Bugfix] message banner hierarchy and rewards card size on smaller screens

[ifbarrera]

📲 What

Fixes two small bugs:

• a bug where the message banner was being presented below other view's added on the PledgeViewController
• bug where the width of the RewardCell is awkwardly large on small (SE) screens

🤔 Why

Polish & fixes.

🛠 How

• guarantee that the MessageBanner is brought to to the front before it's displayed
• add some special logic to reduce the width of the RewardCell for screens with smaller bounds

👀 See

✅ Acceptance criteria

• Logged in, make sure you have the Native Checkout Pledge View feature flag turned ON, navigate to any project. Turn off your internet (you can do this by turning airplane mode on your device to ON). Then, select any reward.
  PASS You should not see any cards loaded in. Then, after a few seconds, you should see an error banner appear with the message "Something went wrong".
• on iPhone SE, with the "Native Checkout" feature flag turned ON navigate to the Rewards screen. Verify that the first reward is fully visible within the bounds of the screen.

[dusi]

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