Handle Vega and Vega-Lite media types when unbundling

[nokome]

In the unbundle method we handle Plotly JSON:

jupita/src/index.ts

Lines 449 to 455 in a4b5757

	public unbundle(bundle: Record<string, any>): schema.Node {
	const plotly = bundle['application/vnd.plotly.v1+json']
	if (plotly !== undefined) {
	// A Plotly, interactive image.
	// A `contentUrl` is required and using an empty string can cause
	// problems elsewhere. So we use a placeholder which also tells the user
	// if there were issues rendering the Plotly data.

This should be expanded to handle other visualization JSON formats, specifically application/vnd.vega.v3+json and application/vnd.vegalite.v2+json (and their other versions).

[nokome]

To do this we may have to alt.renderers.enable('mimebundle'), see https://altair-viz.github.io/user_guide/display_frontends.html#altair-s-renderer-framework