fix: appbar header ignores border bottom radius

[josemak25]

Summary

This fix Implements: #3569

• Add fix for app bar header custom styles
  • This change addresses styles like border bottom radius on the app bar

Test plan

1. Start the example app

2. Click on the Appbar

3. Enable custom color switch

4. Enable Elevated

5. And lastly pass your custom styles to the app bar header

   <Appbar.Header elevated={true} style={{ borderBottomLeftRadius: 16, borderBottomRightRadius: 16 }}>
      <Appbar.Content title="My Title" />
   </Appbar.Header>

screenshot from web

screenshot from web

[callstack-bot]

Hey @josemak25, thank you for your pull request 🤗. The documentation from this branch can be viewed here.

[github-actions]

The mobile version of example app from this branch is ready! You can see it here.