* Set split node's range to minimum of ext and split factor or split nparts, but only when PassDownDomain is called with allow_missing == false, i.e. by InferBound.  Add a helper PassUpThreadBinding() to get a map telling whether an IterVar has at least one leaf IterVar deriving from it binding to a thread. Add two unit tests.

* Enhance LoopVectorizer for vectorizing by 0.  Found at least one case from testtopi/tests/python/test_topi_transform.py::test_tile.

* Revert changes vectorize_loop.cc; when parent's ext is zero, set split's range to the factor or nparts.

* Update with comments.

* Refactor the ext tightening predicate.

* Fix reference types.

* Integrate tvm.te changes.

* Trivial comment change to trigger CI.

* Trivial comment correction to trigger testing.