Share tangent space matrix between regular and clearcoat normals

In case a material has both regular and clearcoat normal maps and is using vertex tangents, we can compute the tangent space matrix made out of the three basis vectors once and use it for both regular and clearcoat normals.

src/renderers/shaders/ShaderChunk/clearcoat_normal_fragment_maps.glsl.js

@@ -6,8 +6,7 @@ export default /* glsl */`
 
 	#ifdef USE_TANGENT
 
-		mat3 vClearcoatTBN = mat3( tangent, bitangent, clearcoatNormal );
-		clearcoatNormal = normalize( vClearcoatTBN * clearcoatMapN );
+		clearcoatNormal = normalize( vTBN * clearcoatMapN );
 
 	#else
 

src/renderers/shaders/ShaderChunk/normal_fragment_begin.glsl.js

@@ -29,6 +29,12 @@ export default /* glsl */`
 
 		#endif
 
+		#if defined( TANGENTSPACE_NORMALMAP ) || defined( USE_CLEARCOAT_NORMALMAP )
+
+			mat3 vTBN = mat3( tangent, bitangent, normal );
+
+		#endif
+
 	#endif
 
 #endif

src/renderers/shaders/ShaderChunk/normal_fragment_maps.glsl.js

@@ -25,7 +25,6 @@ export default /* glsl */`
 
 	#ifdef USE_TANGENT
 
-		mat3 vTBN = mat3( tangent, bitangent, normal );
 		normal = normalize( vTBN * mapN );
 
 	#else