[draft] Add hover publisher, configurable from UI publisher

[schwartzmx]

• This adds an ability to configure hover from UI publisher, although there are some differences in that this publisher relies upon mouseover (hard reliance), and click (maybe optionally if we want to relax that).

Open to suggestions on how to configure this without complicating the types/reliance on target listener api supported events.

• Ideally this is:
  • configurable as other UI events via init
  • supports additional event-specific configuration
  • could enable underlying events it depends on automatically (wish, doesn't do this yet)
  • not need to match existing target api event configuration

Example in test app: