Merge Google Maps handling in Single Field Formatter and Common Map

On a more general level, one could of course ask the question, whether geolocation field should bother to handle Google maps in the first place. Something like https://www.drupal.org/project/gmap might be more suited. But I don't see them or any alternative around the corner, so I guess that sticks with us for now.

v1 - Form handling merged in a new trait.

This patch does a number of things:
- fixes some more eslint warnings
- moves JS closer to Drupal standards (camelCase, use Drupal prefix, more documentation)
- lets the commonMap handler run of the geolocation core JS instead of reproducing its functionality
- all of the above patch, which is
-- introduce new googleMapsTrait
-- fetch and process settings in that trait
-- let the field formatter and views style use said trait

And here's the final thing with Google map styles added.