Add stadia outdoor style with metadata

* `style-microg-normal-stadia.json` is a variant with Stadia custom layers.

* `style-microg-normal-mapbox.json` is a historic, unmaintained variant for use with Mapbox.

* `style-microg-satellite-*.json` is the same, but with a satellite layer (the stadia variant is almost pure openmaptiles, but openmaptiles does not specify a satellite layer).

* `style-stadia-outdoors.json` is identical to Stadia's Outdoors style, but with added microG metadata.

* `sprite_sources` files can be generated to a single sprite file as found in the app's assets using `spreet` (see below).

* PBF files for fonts can be generated using `build_pbf_glyphs` from the `fonts` folder.

## Legal

* based on Mapbox Basic, part of the Mapbox Open Styles, licensed under

* normal and satellite microG styles based on Mapbox Basic, part of the Mapbox Open Styles, licensed under

    * Style code: BSD license

    * Style virtual features / design: CC BY 3.0

    * Reference: https://github.com/mapbox/mapbox-gl-styles/blob/master/LICENSE.md

	* Style design: CC-BY 4.0

	* Reference: https://stadiamaps.com/attribution/

* fonts: Roboto family, licensed Apache 2.0, https://fonts.google.com/specimen/Roboto/about

* outdoor style based on https://docs.stadiamaps.com/map-styles/outdoors/#__tabbed_1_2

    * Style code: BSD 3-Clause License

	* Style design: CC-BY 4.0

	* Reference: https://stadiamaps.com

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        context.assets.open(

            if (BuildConfig.STADIA_KEY.isNotEmpty()) when (mapType) {

                GoogleMap.MAP_TYPE_SATELLITE, GoogleMap.MAP_TYPE_HYBRID -> "style-microg-satellite-stadia.json"

                // TODO GoogleMap.MAP_TYPE_TERRAIN -> …

                GoogleMap.MAP_TYPE_TERRAIN -> "style-stadia-outdoors.json"

                //MAP_TYPE_NONE, MAP_TYPE_NORMAL,

                else -> "style-microg-normal-stadia.json"

            } else when (mapType) {