Dart 3 support & Fix icon white line and add shadow for dark theme

[Eimji]

Hello,

Thanks for your great work.

I would like to submit two fixes with icons in the navigation bar:

• look at an icon carefully, and you will observe there is a white line (at the top edge of the navigation bar);
• add shadow for selected icon for dark themes

Thanks.

[Eimji]

Hello, Could you merge this PR please?

Changelog:

• Update dependencies( & support for Dart 3)
• Migrate the example to to the V2 embedding
• Fix UI issues (cf my previous message)

Thanks.