[mlir] Change DenseArrayAttr to TensorType

Previously, DenseArrayAttr used VectorType for its shaped type.
VectorType is problematic for arrays because it doesn't support zero
dimensions, meaning that an empty array would have `vector<i32>` as its
type. ElementsAttr would think that an empty dense array is size 1, not
0. This patch switches over to TensorType, which does support zero
dimensions.

Fixes #56860

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D130921