Cleanup: Spelling Mistakes

This patch fixes many minor spelling mistakes, all in comments or
console output. Mostly contractions like can't, won't, don't, its/it's,
etc.

Differential Revision: https://developer.blender.org/D11663

Reviewed by Harley Acheson

source/blender/blenkernel/intern/mesh_validate.c

@@ -1441,7 +1441,7 @@ static void mesh_calc_edges_mdata(MVert *UNUSED(allvert),
         med->flag |= ME_LOOSEEDGE;
       }
 
-      /* order is swapped so extruding this edge as a surface wont flip face normals
+      /* order is swapped so extruding this edge as a surface won't flip face normals
        * with cyclic curves */
       if (ed->v1 + 1 != ed->v2) {
         SWAP(uint, med->v1, med->v2);