Tensor TriangleMesh IO

[reyanshsolis]

This change is 

[update-docs[bot]]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[ZhengyuDiao]

Now I directly do a memory copy of the whole vertex buffer from assimp, but the triangle in assimp is stored as a struct and can not use memcpy to create triangle tensor in open3d.

[yxlao]

Material and UV support remain to be added. LGTM after CI.