Recalculates the normals of the Mesh from the triangles and vertices.
After modifying the vertices it is often useful to update the normals to reflect the change. Normals are calculated from all shared vertices.
Imported Meshes sometimes don't share all vertices. For example, a vertex at a UV seam is split into two vertices, so the RecalculateNormals function creates normals that are not smooth at the UV seam.
Note that RecalculateNormals does not generate tangents automatically, so bumpmap Shaders do not work with the Mesh after calling RecalculateNormals. However, you can provide your own tangents.