Native GTK4/libadwaita interface for Linux phones

[x-vlad-x]

Hi! I've built a native GNOME interface (GTK4 + libadwaita) for Organic Maps, aimed at Linux phones (developed on a FuriLabs FLX1s with Phosh) and also usable on desktop GNOME. It follows the Android app's UX: full-screen map in a GtkGLArea (drape on its own GLES3 contexts), the core's touch gestures, search, place page, routing and turn-by-turn navigation with voice, map downloader, bookmarks and tracks, layers and settings, all translated via the existing data/strings. It uses the unmodified core plus a small CMake hook, and keeps Qt6Core/Network for the existing Qt platform layer.

Screenshots and current code: https://github.com/x-vlad-x/organicmaps-gtk
Related: organicmaps/organicmaps#6624, organicmaps/organicmaps#5305, organicmaps/organicmaps#8390

After an email exchange with @biodranik, I'd like to contribute it upstream rather than maintain a fork. Before opening PRs I'd like to confirm:

1. a top-level gtk/ directory next to qt/, built with a CMake option (e.g. BUILD_GTK_APP, off by default) and a CI job;
2. how it should be shipped (a separate Flathub app for Linux phones, or part of app.organicmaps.desktop) and which app ID it should use;
3. a series of PRs: build option + map view with touch gestures, then search, place page, routing/navigation, downloader, bookmarks, settings;
4. parts of the code were generated with an LLM assistant (Claude) under my direction; I reviewed and tested everything on device and will mark it in each PR, as PR_GUIDE asks. Please tell me if that is a problem for this contribution.

Happy to adjust anything to fit the project's plans 😊