[EXPERIMENTAL] replace map-div with `gmp-map` custom element

[usefulthink]

This is an experiment to use the gmp-map custom element instead of a plain div element in the renderer.

The main reason to make this switch once the google maps web-components are stable is to allow interoperability with other web-components like the ones from the @googlemaps/extended-component-library package.

It looks like this will happen some time later this year, but probably after the 1.0 release.

Initial tests look promising though, I didn't get around to fix the unit-tests, but nothing seems seriously broken from a quick look. Next would be to test if this works together with other web-components.