[mlir][mesh] Use tensor shape notation for the shape of a cluster (#73826)

Examle:

substitute
mesh.cluster @mesh0(rank = 2, dim_sizes = [0, 4])

with
mesh.cluster @mesh0(rank = 2, dim_sizes = ?x4)

Same as tensor/memref shapes. The only difference is for 0-rank shapes.
With tensors you would have something like `tensor<f32>`. Here to avoid
matching an empty string a 0-rank shape is denoted by `[]`.