Sidenav styles review

[GomezIvann]

Checklist

• Build process is done without errors and all tests pass in the /lib directory.
• Self-reviewed the code before submitting.
• Meets accessibility standards.
• Added/updated documentation to /website as needed.
• Added/updated tests as needed.

Purpose
Update sidenav styling to make the different states of a sidenav item (collapsable groups and links) more visual, intuitive and consistent.

Description
Summary of changes:

• Token values updated. Specs and affected files have also been updated.
• Reimplementation of the last use of the legacy API React.Children. This required a change in the functionality of the Sidenav regarding the sections of the component, which now are separated between dividers only when using DxcSidenav.Section.