[mlir][transform] Extend `MaskedVectorizeOp` to work for regular vectorization too

This patch extends MaskedVectorizeOp so that it can be used for
"regular" (as opposed to "masked") vectorization as well. While we can
already use VectorizeOp for "regular" vectorization, that Op will also
apply various patterns on top of vectorization. That means that at the
moment, when testing the vectorizer with VectorizeOp, we are effectively
testing "vectorization + patterns", i.e. 2 things at a time.

With these updates, you can trigger "regular" vectorization with
MaskedVectorizeOp by simply skipping the vector sizes:

  transform.structured.masked_vectorize %target : !transform.any_op

Following this change we should probably also rename this Op.

Differential Revision: https://reviews.llvm.org/D157774