ref(dashboards): Namespaced Widget components

[gggritso]

A big re-structure of the components that make up our standard widgets. Improves clarity (simpler component names), removed junk (single-use components that don't need their own files) reduces the number of imports (components are namespaced), and adds more documentation.

Changes

There are a few changes in this PR, all linked together. The easiest way to explain them is in context, so here's an example, taken straight from the new documentation:

// No more `WidgetLayout`. Just `Widget` is clearer in its purpose.
<Widget
  // No need to import `WidgetTitle` component. Use the namespaced `Widget.TextTitle`
  Title={<Widget.TextTitle title="epm() : /insights/frontend/assets" />}
  Actions={
    // New `Widget.Toolbar` ensures spacing of the elements
    <Widget.Toolbar>
      // We used to have a `WidgetButton` component, but it was only used in one place and didn't really provide any value
      <Button size="xs">Say More</Button>
      <Button size="xs">Say Less</Button>
      // `Widget.Description` for rendering description tooltips
      <Widget.Description
        title="epm() : /insights/frontend/assets"
        description="Events received, tracked per minute"
      />
    </Widget.Toolbar>
  }
  Visualization={
    isLoading ? (
      // No guesswork for how to render placeholders! Visualizations always have a `.Placeholder` component attached to them
      <TimeSeriesWidgetVisualization.Placeholder />
    ) : hasError ? (
      // Namespaced `Widget.Error` component
      <Widget.Error error="Oh no!" />
    ) : (
      <TimeSeriesWidgetVisualization
        visualizationType="line"
        timeSeries={[sampleDurationTimeSeries]}
      />
    )
  }
  Footer={<span>This data is incomplete!</span>}
/>

[JonasBa]

I much prefer this sort of API, a bit more tedious to write, but easier to follow, understand, and ultimately a lot more flexible too!

[gggritso]

@JonasBa makes sense! I'm not very sensitive to polluting autocomplete since it also includes the paths, but I agree that for very generic names like "Toolbar" this is a good idea. I think I address your naming suggestions wholesale, but let me know if I missed anything 🙏🏻

[JonasBa]

Nice work @gggritso