Identify the app in the tile request User-Agent

[afarber]

Tile requests sent the same User-Agent for every app, OpenMapView/<version> (https://github.com/afarber/OpenMapView). The OSM tile usage policy asks for a User-Agent that identifies the application. If one app overused the tile servers and OSM blocked that string, every app using OpenMapView would lose its tiles. The base map User-Agent also could not be changed, unlike overlays, which can override UrlTileProvider.getUserAgent().

Now the User-Agent includes the app package name, for both the base map and overlays:

OpenMapView/0.17.1 (com.example.app; https://github.com/afarber/OpenMapView)

• New internal UserAgent object, filled in from context.packageName by every MapController (it is process-wide because UrlTileProvider has no Context)
• TileDownloader and the default UrlTileProvider.getUserAgent() use it; subclasses that override getUserAgent() are unaffected
• The build now generates only LIBRARY_VERSION
• docs/PERFORMANCE.md and docs/REPLACING_GOOGLE_MAPS.md describe the new header

No public setter is added: the package name already identifies the app, and the Google Maps API has nothing like it. One can be added later if someone needs a custom base map User-Agent.

Tests

• UserAgentTest: format with and without a package name, and MapController sets the package name
• TileDownloaderTest and UrlTileProviderTest: base map and overlay requests send the app User-Agent