Navigation Menu: apply colors using block attributes

[retrofox]

Description

It applies the colors using the block attributes instead of using the textColor and backgroundColor properties.

Fixes #18366

How has this been tested?

Following the issue instructions:

To reproduce
Steps to reproduce the behavior:

1. Create a post
2. Create a navigation menu block
3. Set background and foreground colors
4. Save and publish the post
5. Go to Appearance -> Themes and change the theme
6. Go back to the post you created with the navigation block
7. See error -> colours are not there anymore

Expected behavior
I expect the colours to be saved even if I switch themes.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[draganescu]

Works and fixes the problem, color settings are preserved between switching themes.

[retrofox]

Thanks, Andrei.