Add Functionality for Tooltips / Data Labels to be always visible for Circle and Choropleth Layers

[samgehret]

[otravers]

This will come handy! Last time I checked, none of Power BI's default maps (ruling out rolling your own in R or Python) support this without using horrible workarounds as described here: https://mitchellpearson.com/2018/08/19/how-to-add-data-labels-to-maps-in-power-bi/

[otravers]

The following ticket is almost a requisite dependency otherwise things will often look raw: https://github.com/mapbox/mapboxgl-powerbi/issues/211