TriangularFEMForceField Performance optimization

[Alico10]

For large displacements method: initLarge: "mstate->read" should return a reference instead of coord vector, this can significantly improve initialization performance, especially when the mesh is relatively large. I suggest checking the similar issues again. applyStiffnessLarge: TriangleInformation::rotation and its inverse right multiplication coord can be optimized，just like how we did in TriangleFEMUtils.

[alxbilger]

I agree. I'll make a Pull Request soon. Thanks.

[epernod]

@alxbilger do you confirm you fixed that in the PR and we can close this issue?