[MLIR] Refactor to create vectorization convOp precondition check (llvm#130181)

In corner situations, the vectorization pass may face to lower a conv2d
op and assert in a completely irrelevant location in
vectorizeConvolution() subroutine.

~~This PR rejects the conv2d op early and make the asserted routine to
return failure as a defensive workaround.~~

In addressing this, the PR moved all condition check away from the
`Conv1dGenerator` into the `convOpPreconditionCheck()` function. This
makes the unsupported ops such as conv2d to be rejected early and leave
a cleaner `Conv1dGenerator` constructor.

Author: jerryyin