[Lens]: Embeddability API: Add callbacks for event handlers

[flash1293]

Currently chart events in Lens are translated into ui actions in the embeddable. This makes sense for the dashboard integration, but in case of embedded Lens visualizations using the exposed EmbeddableComponent, integration is easier if it's possible to pass in callback functions which are called directly.

This includes:

• Extending EmbeddableComponentProps/LensEmbeddableInput with callbacks: onBrush(data: LensBrushEvent['data']): void etc.
• In x-pack/plugins/lens/public/editor_frame_service/embeddable/embeddable.tsx, in handleEvent check whether there is a callback passed in via input - if that's the case call it instead of execution an action
• Provide support for the following events: brushing, filtering, table row click, edit event (sorting/resizing)
• Also, provide a callback for changes in loading state (if expression changes and re-renders, loading state becomes true, once onData$ gets fired from the expression renderer component, it becomes false again.)

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)