chore: class com.vaadin.flow.component.sidenav.SideNavItemContainer has been made public.

[ovsyannykov]

Description

The public modifier for the com.vaadin.flow.component.sidenav.SideNavItemContainer class makes it possible to use its methods, in particular "public void addItem(SideNavItem... items)", for both SideNav and SideNavItem, which simplifies the code for creating a hierarchical menu.

Type of change

• [ ] Bugfix
• [x] Feature

Issue

#5089 Please make The SideNavItemContainer class public

Checklist

• [x] I have read the contribution guide: https://vaadin.com/docs/latest/contributing/overview
• [x] I have added a description following the guideline.
• [x] The issue is created in the corresponding repository and I have referenced it.
• [x] I have added tests to ensure my change is effective and works as intended - no need.
• [x] New and existing tests are passing locally with my change.
• [x] I have performed self-review and corrected misspellings.
• [ ] I have not completed some of the steps above and my pull request can be closed immediately.

Additional for Feature type of change

• [ ] Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[CLAassistant]

All committers have signed the CLA.

[ugur-vaadin]

Closing in favour of https://github.com/vaadin/flow-components/pull/7266, which converts the class to an interface.