Allow setting hoverformat for lat, lon, and text values in maps

[jackparmer]

Similar to #1383, but for mapbox-gl and D3 maps:

[etpinard]

Now doable using hovertemplate e.g: https://codepen.io/etpinard/pen/oVMLMm

Not sure it's worth adding an attribute similar to zhoverformat for lon and lat formatting.

[jackparmer]

wow, very cool!

[etpinard]

cc #2618 - which is also "doable" using hovertemplate w/o needing an new attribute(s).

We'll need to discuss how much we want to "solve" everything using hovertemplate or adding more hover-label-content-related attributes is still the way to go.

[gvwilson]

Hi - this issue has been sitting for a while, so as part of our effort to tidy up our public repositories I'm going to close it. If it's still a concern, we'd be grateful if you could open a new issue (with a short reproducible example if appropriate) so that we can add it to our stack. Cheers - @gvwilson