fix: clean submenu items classes in Nest #11467

[ncoden]

Description

When a DropdownMenu (or an other menu with nested items) is destroyed, submenu item classes like is-<type>-submenu-item are not removed, because only direct childs are targeted by the cleaning function.

This pull requests add [data-submenu] > li to ensure that submenu items are cleaned too.

Closes #11467

Types of changes

• Documentation
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to change)

Checklist (all required):

• I have read and follow the CONTRIBUTING document.
• There are no other pull request similar to this one.
• The pull request title is descriptive.
• The template is fully and correctly filled.
• The pull request targets the right branch (develop or develop-v...).
• My commits are correctly titled and contain all relevant information.
• My code follows the code style of this project.
• I have updated the documentation accordingly to my changes (if relevant).
• I have added tests to cover my changes (if relevant).
• All new and existing tests passed.