Create a copy of a mesh where each triangle has vertices with normals outward from the triangle

FlattenMeshNormalsMenu.cs

using UnityEngine;
using UnityEditor;

static public class FlattenMeshNormalsMenu
{
    [MenuItem("GameObject/Flatten Mesh Normals", true)]
    static bool GameObject_FlattenMeshNormals_validate()
    {
        var go = Selection.activeObject as GameObject;
        if (go == null) return false;

        return go.GetComponent<MeshFilter>() != null;
    }

    [MenuItem("GameObject/Flatten Mesh Normals", false, 10)]
    static void GameObject_FlattenMeshNormals()
    {
        var mf = (Selection.activeObject as GameObject).GetComponent<MeshFilter>();

        mf.sharedMesh = flattenNormals(mf.sharedMesh);
    }

    static Mesh flattenNormals(Mesh mesh)
    {
        var verts = new Vector3[mesh.triangles.Length];
        var tris = new int[mesh.triangles.Length];

        for (int i = 0; i < mesh.triangles.Length; ++i) {
            verts[i] = mesh.vertices[mesh.triangles[i]];
            tris[i] = i;
        }

        var ret = new Mesh();

        ret.vertices = verts;
        ret.triangles = tris;

        ret.RecalculateNormals();
        ret.RecalculateTangents();
        ret.RecalculateBounds();

        return ret;
    }
}