Fix support for EXT_mesh_gpu_instancing

bufferView is not a valid attribute; it looks like the code was probably
copied from Draco where this attribute is valid.

Also we were missing skip_json for both this extension and Draco; this
can be necessary to skip extras data.

cgltf.h

@@ -559,7 +559,6 @@ typedef struct cgltf_draco_mesh_compression {
 } cgltf_draco_mesh_compression;
 
 typedef struct cgltf_mesh_gpu_instancing {
-	cgltf_buffer_view* buffer_view;
 	cgltf_attribute* attributes;
 	cgltf_size attributes_count;
 } cgltf_mesh_gpu_instancing;
@@ -2864,6 +2863,10 @@ static int cgltf_parse_json_draco_mesh_compression(cgltf_options* options, jsmnt
 			out_draco_mesh_compression->buffer_view = CGLTF_PTRINDEX(cgltf_buffer_view, cgltf_json_to_int(tokens + i, json_chunk));
 			++i;
 		}
+		else
+		{
+			i = cgltf_skip_json(tokens, i+1);
+		}
 
 		if (i < 0)
 		{
@@ -2889,11 +2892,9 @@ static int cgltf_parse_json_mesh_gpu_instancing(cgltf_options* options, jsmntok_
 		{
 			i = cgltf_parse_json_attribute_list(options, tokens, i + 1, json_chunk, &out_mesh_gpu_instancing->attributes, &out_mesh_gpu_instancing->attributes_count);
 		}
-		else if (cgltf_json_strcmp(tokens + i, json_chunk, "bufferView") == 0)
+		else
 		{
-			++i;
-			out_mesh_gpu_instancing->buffer_view = CGLTF_PTRINDEX(cgltf_buffer_view, cgltf_json_to_int(tokens + i, json_chunk));
-			++i;
+			i = cgltf_skip_json(tokens, i+1);
 		}
 
 		if (i < 0)
@@ -6411,7 +6412,6 @@ static int cgltf_fixup_pointers(cgltf_data* data)
 
 		if (data->nodes[i].has_mesh_gpu_instancing)
 		{
-			CGLTF_PTRFIXUP_REQ(data->nodes[i].mesh_gpu_instancing.buffer_view, data->buffer_views, data->buffer_views_count);
 			for (cgltf_size m = 0; m < data->nodes[i].mesh_gpu_instancing.attributes_count; ++m)
 			{
 				CGLTF_PTRFIXUP_REQ(data->nodes[i].mesh_gpu_instancing.attributes[m].data, data->accessors, data->accessors_count);

cgltf_write.h

@@ -977,7 +977,6 @@ static void cgltf_write_node(cgltf_write_context* context, const cgltf_node* nod
 
 		cgltf_write_line(context, "\"EXT_mesh_gpu_instancing\": {");
 		{
-			CGLTF_WRITE_IDXPROP("bufferView", node->mesh_gpu_instancing.buffer_view, context->data->buffer_views);
 			cgltf_write_line(context, "\"attributes\": {");
 			{
 				for (cgltf_size i = 0; i < node->mesh_gpu_instancing.attributes_count; ++i)