Allows setting prefersLargeTitles as well as hiding the shadow/bottom shadow border on the ActionBar. Changes no current defaults, just extra options to customize.

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

Currently you could use loaded event to grab ActionBar reference to set it's prefersLargeTitles property on the UINavigationBar as well as modify it's appearance.

What is the new behavior?

This introduces 2 new ActionBar attributes:

• iosLargeTitle: boolean (keeps current default, which is false).
• iosShadow: boolean (keeps current default, which is true).

Introduces no breaking changes - keeps existing behavior while providing easy declarative options to customize.

closes #9046
closes #5904

With iosLargeTitle="true" iosShadow="false":
https://github.com/user-attachments/assets/3e49e358-32c1-4b69-927f-5ce32744d794

With just iosLargeTitle="true", keeping current shadow default:
https://github.com/user-attachments/assets/28f9d02a-d41f-4e89-a231-157ea88389da

With just iosShadow="false":
https://github.com/user-attachments/assets/3228088d-478a-464f-baa3-34eeb3b5ef33