This introduces `BKE_mesh_to_bmesh_ex()`, which exposes all of the `BMeshFromMeshParams` parameters to the caller. This is required to enable the `calc_face_normal` flag, which is required for the Bevel modifier. This also introduces `BKE_bmesh_to_mesh()`, which allocates a new `Mesh`, converts the `BMesh` to it, and returns it. The returned mesh is owned by the caller.