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/python/mathutils/mathutils_Vector.c

@@ -2300,7 +2300,7 @@ static int Vector_length_set(VectorObject *self, PyObject *value)
   dot = dot_vn_vn(self->vec, self->vec, self->size);
 
   if (!dot) {
-    /* cant sqrt zero */
+    /* can't sqrt zero */
     return 0;
   }