feat: adding new and improved slots-controller

Description

(this PR updates legacy-next branch, so all current projects can utilize it)

Adding new and improved slots-controller.

This controller allows cloning slots into the shadow DOM, by calling a function inside render() of the component. Any changes in the light DOM trigger requestUpdate() and thus re-cloning of the slots into the shadow DOM. The controller dispatches Click events that are triggered in the cloned slots in shadow DOM to the equivalent light DOM slot.

Type of change

Please delete options that are not relevant.

[ ] Bug fix (non-breaking change which fixes an issue)
[x] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

[ ] Visual Testing
[ ] Automated Testing
[ ] Accessibility Testing

Checklist

[x] My code follows the style guidelines of this project
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation
[x] My changes generate no new warnings
[ ] I have added tests that prove my fix is effective or that my feature works
[ ] New and existing unit tests pass locally with my changes
[ ] Any dependent changes have been merged and published in downstream modules

phase2 / outline