[mlir] Add vectorize_nd_extract attribute to the masked_vectorize Op

This patch simply adds `vectorize_nd_extract` (that's currently only
used for the `vectorize` Op) to `masked_vectorize`. A test is added to
verify that it works as expected - it prevents the masked vectorisation
of `tensor.extract`, which is currently not supported.

Differential Revision: https://reviews.llvm.org/D142634