Render: default roughness distribution to Multiscatter GGX

for glass, glossy and principled BSDF. It is more energy-preserving than
GGX, and with the albedo scaling instead of random walk (888bdc1419) the
render time stays reasonable.

Task: #99447

Pull Request: https://projects.blender.org/blender/blender/pulls/111267

source/blender/blenloader/intern/versioning_defaults.cc

@@ -608,6 +608,7 @@ void BLO_update_defaults_startup_blend(Main *bmain, const char *app_template)
           bNodeSocketValueFloat *roughness_data = static_cast<bNodeSocketValueFloat *>(
               roughness_socket->default_value);
           roughness_data->value = 0.5f;
+          node->custom1 = SHD_GLOSSY_MULTI_GGX;
           node->custom2 = SHD_SUBSURFACE_RANDOM_WALK;
           BKE_ntree_update_tag_node_property(ma->nodetree, node);
         }

source/blender/nodes/shader/nodes/node_shader_bsdf_glass.cc

@@ -22,7 +22,7 @@ static void node_declare(NodeDeclarationBuilder &b)
 
 static void node_shader_init_glass(bNodeTree * /*ntree*/, bNode *node)
 {
-  node->custom1 = SHD_GLOSSY_BECKMANN;
+  node->custom1 = SHD_GLOSSY_MULTI_GGX;
 }
 
 static int node_shader_gpu_bsdf_glass(GPUMaterial *mat,

source/blender/nodes/shader/nodes/node_shader_bsdf_glossy.cc

@@ -36,7 +36,7 @@ static void node_shader_buts_glossy(uiLayout *layout, bContext * /*C*/, PointerR
 
 static void node_shader_init_glossy(bNodeTree * /*ntree*/, bNode *node)
 {
-  node->custom1 = SHD_GLOSSY_GGX;
+  node->custom1 = SHD_GLOSSY_MULTI_GGX;
 }
 
 static int node_shader_gpu_bsdf_glossy(GPUMaterial *mat,

source/blender/nodes/shader/nodes/node_shader_bsdf_principled.cc

@@ -137,7 +137,7 @@ static void node_shader_buts_principled(uiLayout *layout, bContext * /*C*/, Poin
 
 static void node_shader_init_principled(bNodeTree * /*ntree*/, bNode *node)
 {
-  node->custom1 = SHD_GLOSSY_GGX;
+  node->custom1 = SHD_GLOSSY_MULTI_GGX;
   node->custom2 = SHD_SUBSURFACE_RANDOM_WALK;
 }