Use AHashMap for SurfaceTool

[Nazarwadim]

Makes index method 6x faster and generate_normals 3x faster.

Tested in https://github.com/godotengine/godot-demo-projects/tree/master/3d/voxel.

In the _generate_chunk_mesh method of the Chunk class, I used Time.get_ticks_usec to get the elapsed time.

Master:

Total mesh generation time:1990
Generate normals time:132
index time:798
 
Total mesh generation time:2402
Generate normals time:150
index time:980
 
Total mesh generation time:1976
Generate normals time:122
index time:786
 
Total mesh generation time:2403
Generate normals time:158
index time:967
 
Total mesh generation time:2205
Generate normals time:132
index time:875
 
Total mesh generation time:2415
Generate normals time:154
index time:970
 
Total mesh generation time:2590
Generate normals time:165
index time:1039

Current PR:

Total mesh generation time:1556
Generate normals time:69
index time:182
 
Total mesh generation time:1350
Generate normals time:60
index time:157
 
Total mesh generation time:1558
Generate normals time:72
index time:184
 
Total mesh generation time:1087
Generate normals time:51
index time:132
 
Total mesh generation time:1408
Generate normals time:61
index time:161
 
Total mesh generation time:1709
Generate normals time:90
index time:153
 
Total mesh generation time:1348
Generate normals time:59
index time:156

It is worth noting that GDScript has now become the bottleneck, and if we were to do the same generation in C#, the total generation time would decrease many times.

[clayjohn]

Overall this looks great and the benchmarking results are fantastic! I just left one comment with a question + a suggestion

[clayjohn]

The code looks good.

I tested locally using an OBJ version of this mesh (https://sketchfab.com/3d-models/thunderjaw-from-horizon-zero-dawn-34acb03c841247d28aaa80204f1f52b2). SurfaceTool is used to import OBJ files, and it always calls index. So its a good way to test real world performance without the overhead of GDScript.

I saw about a 5% decrease in overall import time for the file, which is pretty significant.

The final vertex count is exactly the same. So this should be totally safe

[akien-mga]

Thanks!