PanelContainerImpl should be moved from internal

## Feature Request

**Is your feature request related to a problem? Please describe.**
Make the PanelContainerImpl class public (not in internal) so new custom PanelContainers (Like outside of tabs and accordions) can be created without duplicated the underlying classes

**Describe the solution you'd like**
Move com.adobe.cq.wcm.core.components.internal.models.v1.PanelContainerImpl to com.adobe.cq.wcm.core.components.util.AbstractPanelContainerImpl. This is the same spot as the AbstractComponentImpl.

**Are there alternatives?**
There are not

**Documentation**
Users will be able to create custom components that are similar to tabs or accordions without having to duplicate classes

Start by inspecting com.adobe.cq.wcm.core.components.internal.models.v1.PanelContainerImpl and comparing its intended public placement with com.adobe.cq.wcm.core.components.util.AbstractComponentImpl. Trace the existing PanelContainer implementations and references, then verify that the class is available from the requested util package without requiring duplicated underlying classes.

Written by the indexing model from the issue text.