Map::nudgeTransitions no longer depends on client information

Clients no longer need to provide data (eg. if gesturing or in a custom
animation) to Map::nudgeTransitions().

Upon MapContext::renderSync(), a new atomic bool 'needsRepaint' in MapData
allows thread-safe communication between Map and MapContext.

include/mbgl/android/native_map_view.hpp

@@ -49,7 +49,7 @@ public:
     void enableFps(bool enable);
     void updateFps();
 
-    void onInvalidate(bool inProgress);
+    void onInvalidate();
 
     void resizeView(int width, int height);
     void resizeFramebuffer(int width, int height);

include/mbgl/map/map.hpp

@@ -66,11 +66,11 @@ public:
     using StillImageCallback = std::function<void(std::exception_ptr, std::unique_ptr<const StillImage>)>;
     void renderStill(StillImageCallback callback);
 
-    // Triggers a synchronous or asynchronous render.
-    bool renderSync();
+    // Triggers a synchronous render.
+    void renderSync();
 
-    // Nudges transitions one step, possibly notifying of the need for a rerender.
-    void nudgeTransitions(bool forceRerender);
+    // Nudges transitions one step, possibly notifying of the need for a rerender, if any.
+    void nudgeTransitions();
 
     // Notifies the Map thread that the state has changed and an update might be necessary.
     void update(Update update);