Route canvas input policy through platform services

src/app.h

@@ -192,6 +192,8 @@ public:
     [[nodiscard]] bool uses_ppbr_export_data_directory_override() const;
     [[nodiscard]] bool platform_supports_sonarpen() const;
     void start_platform_sonarpen();
+    [[nodiscard]] bool draws_canvas_tip_for_input(kEventSource source, kEventType type) const;
+    [[nodiscard]] float adjust_canvas_input_pressure(float pressure) const;
     void pick_dir(std::function<void(std::string path)> callback);
     void display_file(std::string path);
     void share_file(std::string path);