[VectorOps] Add [insert/extract]element definition together with lowering to LLVM

Similar to insert/extract vector instructions but
(1) work on 1-D vectors only
(2) allow for a dynamic index

  %c3 = constant 3 : index
  %0 = vector.insertelement %arg0, %arg1[%c : index] : vector<4xf32>
  %1 = vector.extractelement %arg0[%c3 : index] : vector<4xf32>

PiperOrigin-RevId: 285792205