[mlir][vector] Support 0-D vector when eliding single element reduction

ElideSingleElementReduction causes assertion failure when we give 0-D vector. It's possible to fold the case by using vector.extractelement op instead. It's originally reported in https://github.com/llvm/llvm-project/issues/60193.

Reviewed By: dcaballe

Differential Revision: https://reviews.llvm.org/D143242