Add tbnMat variable to PBRSurface.glsl

Updated to store tbnMat as a publicly accessible variable in the PBRSurface.glsl struct, that way tbnMat won't need recalculated anywhere else in the shader it is needed.

jme3-core/src/main/resources/Common/ShaderLib/module/PBRSurface.glsl

@@ -10,6 +10,7 @@
         vec3 normal; // normals w/ normalmap
         bool frontFacing; //gl_FrontFacing
         float depth;
+        mat3 tbnMat;
 
         // from texture
         vec3 albedo;
@@ -36,4 +37,4 @@
     #endstruct
     #define PBRSurface StdPBRSurface    
 #endif
-#endif
+#endif