Allow users to access mjrContext.

PiperOrigin-RevId: 836641787
Change-Id: I2f2aee30a047336d1adbe33b7996fee3ec845213

src/experimental/toolbox/renderer.h

@@ -58,6 +58,9 @@ class Renderer {
   // Returns the current, average frame rate.
   double GetFrameRate() const { return fps_; }
 
+  // Returns the render context.
+  const mjrContext& GetContext() const { return render_context_; }
+
  private:
   using TimePoint = std::chrono::time_point<std::chrono::steady_clock>;