Replaced deprecated navigator.platform with navigator.userAgent for platform detection.

[manutdkid77]

This fixes #13156

Description

Browser OS information uses the deprecated method navigator.platform. So I replaced it with navigator.userAgent, exactly the same as how it is used in umbraco v15.

Note: Though the issue is reported for v10 and v11. It is present in v13 LTS as well.

How to test

1. Log into the Umbraco Backoffice.
2. Click on the Help icon in the top right of the screen.
3. View the System Information from the sidebar that appears.
4. Check the Browser (user agent) string

[github-actions]

Hi there @manutdkid77, thank you for this contribution! 👍

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[emmagarland]

Hi @manutdkid77!

Thanks for this contribution! One of the core Collabs team will take a look at it soon 🔜

Best wishes

Emma