core: rename mbgl directories to mln (#4511)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/mln/gfx/backend_scope.hpp

@@ -0,0 +1,38 @@
+#pragma once
+
+namespace mln {
+namespace gfx {
+
+class RendererBackend;
+
+class BackendScope {
+public:
+    /// There are two types of scopes: Creating an "Implicit" scope tells MapLibre
+    /// Native that the supporting windowing system has already activated the
+    /// RenderBackend and that no further actions are required. Creating an "Explicit"
+    /// scope (the default) actually enables the RenderBackend, and disables it when
+    /// the BackendScope is destroyed.
+    enum class ScopeType : bool {
+        Implicit,
+        Explicit,
+    };
+
+    BackendScope(RendererBackend&, ScopeType = ScopeType::Explicit);
+    ~BackendScope();
+
+    // Returns true when there is currently a BackendScope active in this thread.
+    static bool exists();
+
+private:
+    void activate();
+    void deactivate();
+
+    BackendScope* priorScope;
+    BackendScope* nextScope;
+    RendererBackend& backend;
+    const ScopeType scopeType;
+    bool activated = false;
+};
+
+} // namespace gfx
+} // namespace mln