[mlir][Vector][Transforms] Improve the control over individual vector lowerings and transforms

This revision adds vector transform operations that allow us to better inspect the composition
of various lowerings that were previously very opaque.

This commit is NFC in that it does not change patterns beyond adding `rewriter.notifyFailure` messages
and it does not change the tests beyond breaking them into pieces and using transforms instead of
throwaway opaque test passes.

Reviewed By: ftynse, springerm

Co-authored-by: Alex Zinenko <zinenko@google.com>

Differential Revision: https://reviews.llvm.org/D146755