Rework Mesh handling on scene importing.

-Reworked how meshes are treated by importer by using EditorSceneImporterMesh and EditorSceneImporterMeshNode. Instead of Mesh and MeshInstance, this allows more efficient processing of meshes before they are actually registered in the RenderingServer.
-Integrated MeshOptimizer
-Reworked internals of SurfaceTool to use arrays, making it more performant and easy to run optimizatons on.

thirdparty/meshoptimizer/vfetchoptimizer.cpp

@@ -0,0 +1,74 @@
+// This file is part of meshoptimizer library; see meshoptimizer.h for version/license details
+#include "meshoptimizer.h"
+
+#include <assert.h>
+#include <string.h>
+
+size_t meshopt_optimizeVertexFetchRemap(unsigned int* destination, const unsigned int* indices, size_t index_count, size_t vertex_count)
+{
+	assert(index_count % 3 == 0);
+
+	memset(destination, -1, vertex_count * sizeof(unsigned int));
+
+	unsigned int next_vertex = 0;
+
+	for (size_t i = 0; i < index_count; ++i)
+	{
+		unsigned int index = indices[i];
+		assert(index < vertex_count);
+
+		if (destination[index] == ~0u)
+		{
+			destination[index] = next_vertex++;
+		}
+	}
+
+	assert(next_vertex <= vertex_count);
+
+	return next_vertex;
+}
+
+size_t meshopt_optimizeVertexFetch(void* destination, unsigned int* indices, size_t index_count, const void* vertices, size_t vertex_count, size_t vertex_size)
+{
+	assert(index_count % 3 == 0);
+	assert(vertex_size > 0 && vertex_size <= 256);
+
+	meshopt_Allocator allocator;
+
+	// support in-place optimization
+	if (destination == vertices)
+	{
+		unsigned char* vertices_copy = allocator.allocate<unsigned char>(vertex_count * vertex_size);
+		memcpy(vertices_copy, vertices, vertex_count * vertex_size);
+		vertices = vertices_copy;
+	}
+
+	// build vertex remap table
+	unsigned int* vertex_remap = allocator.allocate<unsigned int>(vertex_count);
+	memset(vertex_remap, -1, vertex_count * sizeof(unsigned int));
+
+	unsigned int next_vertex = 0;
+
+	for (size_t i = 0; i < index_count; ++i)
+	{
+		unsigned int index = indices[i];
+		assert(index < vertex_count);
+
+		unsigned int& remap = vertex_remap[index];
+
+		if (remap == ~0u) // vertex was not added to destination VB
+		{
+			// add vertex
+			memcpy(static_cast<unsigned char*>(destination) + next_vertex * vertex_size, static_cast<const unsigned char*>(vertices) + index * vertex_size, vertex_size);
+
+			remap = next_vertex++;
+		}
+
+		// modify indices in place
+		indices[i] = remap;
+	}
+
+	assert(next_vertex <= vertex_count);
+
+	return next_vertex;
+}