Static mesh optimizations support

[japsuu]

Is your feature request related to a problem? Please describe.
Currently, there is no way to combine or optimize meshes for drawing.
Combining meshes would help with reducing draw-calls, and optimizing meshes internally (reordering verts/tris) should help with GPU cache coherency.

Describe the solution you'd like

1. Implement a mesh combining API, that takes multiple materials and meshes as input, and returns a combined mesh.
2. Implement mesh optimization API (similar to Unity's Mesh.Optimize, that internally reorders the vertex data to GPU favorable format.

Mesh combining would most likely also require multi-material-support, where a single mesh can be drawn using multiple different materials.

Describe alternatives you've considered
Not supporting mesh optimizations.
This is also a valid path, since there are offline tools that can be used to optimize meshes.

Additional context
Mesh optimization:

• https://github.com/maxilevi/MeshOptimizer.NET
• https://github.com/amerkoleci/Alimer.Bindings
• https://github.com/Unity-Technologies/AutoLOD