Update Solid and Shell plugins to use FlexComp.

PiperOrigin-RevId: 573755821
Change-Id: I3b8d7fb27f0e940038fa9fd2b26ecc746df4f7ac

plugin/elasticity/solid.h

@@ -44,6 +44,7 @@ class Solid {
 
   static void RegisterPlugin();
 
+  int f0;  // index of corresponding flex
   int i0;  // index of first body
   int nc;  // number of cubes in the grid
   int nv;  // number of vertices (bodies) in the solid
@@ -64,9 +65,11 @@ class Solid {
 
  private:
   Solid(const mjModel* m, mjData* d, int instance, mjtNum nu, mjtNum E,
-        mjtNum damp, const std::vector<int>& simplex);
+        mjtNum damp, const std::vector<int>& simplex,
+        const std::vector<int>& edgeidx);
 
-  void CreateStencils(const std::vector<int>& simplex);
+  void CreateStencils(const std::vector<int>& simplex,
+                      const std::vector<int>& edgeidx);
 };
 
 }  // namespace mujoco::plugin::elasticity