[Lens] Show visualization "skeleton" on empty/loading visualizations

[ghudgins]

Describe the feature:
Instead of an icon an a message, show an empty visualization when there is no data.

Describe a specific use case for the feature:
Empty data case
When I am on a dashboard
And I have selected a date range that has no data
I need to see empty visualizations that represent the visualizations I should see
So I can visually see the structure of the dashboard even if there's no data
And so panels don't appear "broken" but rather don't currently have data

Data is loading case
When I am loading data on a dashboard
I need to see a shell of the visualization while it's loading
So I can see that something is happening
And have an idea of what each panel will look like on completion

Design considerations

• For time axis, filters we will have enough data to render the domain of the vis
• For terms, number histogram we do not know the domain and will have to use stand in
• The legend, metric axis size will be unknown when running on auto and may adjust after the vis loads

[elasticmachine]

Pinging @elastic/kibana-vis-editors @elastic/kibana-vis-editors-external (Team:VisEditors)

[drewdaemon]

Related to #141974