Mesh: add test for isomorphic meshes

In many cases when updating some mesh algorithm, the resulting mesh
might have different indices. Current tests could not detect this and
would complain that the two meshes are different. The meshes_isomorphic
function attempts to solve this problem, by finding a re-ordering of
indices such that the two meshes become equal.

@@ -0,0 +18,4 @@
+ * Convert the mismatch to a human-readable string for display.
+ */
+const char *mismatch_to_string(const MeshMismatch &mismatch);
+

@@ -0,0 +251,4 @@
+    return value1 != value2;
+  }
+  /* The other types are based on floats. */
+  else if constexpr (std::is_same_v<T, float>) {

@@ -0,0 +271,4 @@
+    return false;
+  }
+  else if constexpr (std::is_same_v<T, math::Quaternion> || std::is_same_v<T, ColorGeometry4f>) {
+    const float4 value1_f = static_cast<float4>(value1);

@@ -0,0 +674,4 @@
+     * the mesh is of good enough quality that this doesn't happen. Otherwise, the logic becomes a
+     * lot more difficult. */
+    if (matching_verts.size() != 1) {
+      BLI_assert(false);

@@ -0,0 +717,4 @@
+    return MeshMismatch::NumFaces;
+  }
+
+  std::cout << "domain sizes match" << std::endl;

@@ -45,0 +50,4 @@
+    return !(e1 == e2);
+  }
+
+  friend std::ostream &operator<<(std::ostream &stream, const OrderedEdge &e)

@@ -0,0 +29,4 @@
+ * time algorithm is known). Because we have more information than just connectivity (attributes),
+ * we can compute it in a more reasonable time in most cases.
+ *
+ * \warning This assumes that the mesh is of decent quality: no zero-size edges or faces.

@@ -0,0 +31,4 @@
+ *
+ * \warning This assumes that the mesh is of decent quality: no zero-size edges or faces.
+ */
+std::optional<MeshMismatch> meshes_isomorphic(const Mesh &mesh1,

@@ -0,0 +58,4 @@
+      return "The sets of attribute ids are different";
+    case MeshMismatch::AttributeTypes:
+      return "Some attributes with the same name have different types";
+    default:

@@ -0,0 +233,4 @@
+                             const float threshold,
+                             const int component_i)
+{
+  if constexpr (std::is_same_v<T, int> || std::is_same_v<T, int2> || std::is_same_v<T, bool> ||

@@ -0,0 +843,4 @@
+    return MeshMismatch::FaceTopology;
+  }
+
+  return {};

@@ -36,12 +36,13 @@ struct OrderedEdge {
     return (this->v_low << 8) ^ this->v_high;
   }
 
-  friend bool operator==(const OrderedEdge &e1, const OrderedEdge &e2)

@@ -39,2 +40,3 @@
 {
-  const char *ret = BKE_mesh_cmp(mesh, mesh2, threshold);
+  using namespace blender::bke::mesh;
+  const std::optional<MeshMismatch> mismatch = meshes_isomorphic(*mesh, *mesh2, threshold);

@@ -0,0 +10,4 @@
+ * \ingroup bke
+ */
+
+namespace blender::bke::mesh {