Cleanup: split normal calculation into it's own file

Normals now includes many functions including normal splitting &
custom normal manipulation split this into it's own file
to centralize related functions.

source/blender/blenkernel/BKE_mesh.h

@@ -299,7 +299,7 @@ void BKE_mesh_recalc_looptri_with_normals(const struct MLoop *mloop,
                                           struct MLoopTri *mlooptri,
                                           const float (*poly_normals)[3]);
 
-/* *** mesh_evaluate.c *** */
+/* *** mesh_normals.c *** */
 
 void BKE_mesh_calc_normals_mapping_simple(struct Mesh *me);
 void BKE_mesh_calc_normals_mapping(struct MVert *mverts,
@@ -494,6 +494,8 @@ void BKE_mesh_calc_normals_split_ex(struct Mesh *mesh,
 void BKE_mesh_set_custom_normals(struct Mesh *mesh, float (*r_custom_loopnors)[3]);
 void BKE_mesh_set_custom_normals_from_vertices(struct Mesh *mesh, float (*r_custom_vertnors)[3]);
 
+/* *** mesh_evaluate.c *** */
+
 void BKE_mesh_calc_poly_normal(const struct MPoly *mpoly,
                                const struct MLoop *loopstart,
                                const struct MVert *mvarray,

source/blender/blenkernel/CMakeLists.txt

@@ -190,6 +190,7 @@ set(SRC
   intern/mesh_mapping.c
   intern/mesh_merge.c
   intern/mesh_mirror.c
+  intern/mesh_normals.c
   intern/mesh_remap.c
   intern/mesh_remesh_voxel.c
   intern/mesh_runtime.c

source/blender/bmesh/intern/bmesh_mesh_normals.c

@@ -18,6 +18,8 @@
  * \ingroup bmesh
  *
  * BM mesh normal calculation functions.
+ *
+ * \see mesh_normals.c for the equivalent #Mesh functionality.
  */
 
 #include "MEM_guardedalloc.h"