DOM Inspector Expose Selected Element

**Is your feature request related to a problem? Please describe.**

When using the DOM Inspector, I'd like to know what element is currently selected.

**Describe the solution you'd like**

Exposing an onDOMSelect method or something similar that would fire each time a new element is selected.

**Describe alternatives you've considered**

None

**Additional context**

My goal is to show style details(basically recreating devtools, we're running in a sandboxed environment), so if this is something you're already looking at then its something I can wait on

Start at the DOM Inspector's element-selection handling and trace how the currently selected element is represented. Define the callback or equivalent API and ensure it fires whenever selection changes, including the element details needed by the requester's style-inspection use case. Add or update coverage for selection notifications if the existing component tests provide an entry point.

Written by the indexing model from the issue text.