fixup! [mlir][vector][nfc] Update vector-to-llvm.mlir

* Add missing "split" seperators (`// -----`)
* Capitialize LIT variables (e.g. %[[insert]] --> %[[INSERT]])
* Renamed some func variables to either better align with the convention in the
  file (e.g. `%a` -> `%vec_1d`) or to make sure the name is more
  descriptive (e.g. `%a` -> `%num_elems`)
* Other typos highlighted by Hugo (thanks!)

Author: banach-space