First pass at mjSpec Explorer and Properties windows.

Displays the list of bodies and joints from the mjSpec and displays
values for the selected element.

Functionality is very limited and a bit non-intuitive. However, we want
to get this into our users hands to start getting feedback.

PiperOrigin-RevId: 842228895
Change-Id: I2491cd5e0acaf622110e0f6b8406919024d3607a

src/experimental/studio/app.h

@@ -84,7 +84,7 @@ class App {
 
     // Windows.
     bool help = false;
-    bool info = false;
+    bool stats = false;
     bool chart_cpu_time = false;
     bool chart_dimensions = false;
     bool chart_solver = false;
@@ -106,6 +106,10 @@ class App {
     std::vector<std::string> camera_names;
     std::vector<std::string> speed_names;
 
+    // Spec Properties.
+    mjsElement* element = nullptr;
+    int element_id = -1;
+
     // State.
     int state_sig = 0;
     std::vector<mjtNum> state;
@@ -152,6 +156,8 @@ class App {
   void FileDialogGui();
   void ModelOptionsGui();
   void DataInspectorGui();
+  void SpecExplorerGui();
+  void PropertiesGui();
 
   float GetExpectedLabelWidth();
   std::vector<const char*> GetCameraNames();