Merge branch '1388-stadia-map-style' into 'master'

## The files

* `style-microg-normal-openmaptiles.json` is a pure OpenMapTiles schema version of microG's custom style. The sources are set to Stadia but could be modified to be used with another schema-compliant vendor, e.g. MapTiler.

* `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.

## Resources

### For creating styles

* Tool: https://maputnik.github.io/

* Style spec: https://maplibre.org/maplibre-style-spec/

	* https://maplibre.org/maplibre-style-spec/expressions/

* Style schema: **https://openmaptiles.org/schema/**

* Schema tileset explorer (requires maptiler login): https://cloud.maptiler.com/tiles/v3-openmaptiles/

#### Vendor-specific

* Mapbox

    * https://docs.mapbox.com/data/tilesets/reference/mapbox-streets-v8/

* Stadia

    * https://docs.stadiamaps.com/custom-styles/

    * https://docs.stadiamaps.com/tilesets/

### For converting assets

* https://github.com/flother/spreet

* https://github.com/stadiamaps/sdf_font_tools/tree/main/build_pbf_glyphs

Commands:

```

$ cp style-microg-{satellite,normal}-{mapbox,stadia}.json style-stadia-outdoors.json style-mapbox-outdoors-v12.json ../../play-services-maps-core-mapbox/src/main/assets/

$ spreet sprite_sources/ ../../play-services-maps-core-mapbox/src/main/assets/sprites

$ spreet --retina sprite_sources/ ../../play-services-maps-core-mapbox/src/main/assets/sprites@2x

$ build_pbf_glyphs --overwrite -c fonts/combinations.json fonts/ ../../play-services-maps-core-mapbox/src/main/assets

$ rm -r ../../play-services-maps-core-mapbox/src/main/assets/OpenSans\ Regular # remove temporary files

```

* We combine Open Sans Regular with Roboto Regular so that no glyphs are missing.

* A symbolic link in the assets folder points from the font stack specification "Open Sans Regular,Arial Unicode MS Regular" to "Roboto Regular". It is unclear why MapLibre sometimes tries to access this font and fails rendering entire tiles if it is not present.

The assets are referenced using `asset://` in the style. For using Maputnik, it may be convenient to set the glyphs and sprites source to these Mapbox-hosted sources:

```

    "sprite": "mapbox://sprites/microg/cjui4020201oo1fmca7yuwbor/8fkcj5fgn4mftlzuak3guz1f9",

    "glyphs": "mapbox://fonts/microg/{fontstack}/{range}.pbf",

```

## Legal

* 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

* derivation created by larma

* derivation created by /e/ foundation

* makes use of snippets from [Stadia's variant of OSM Bright](https://docs.stadiamaps.com/map-styles/osm-bright/), also a derivation of Mapbox Open Styles

	* Style code: BSD 3-Clause License

	* 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