[mlir][tosa] Add constant block scaled support (#205506)
This commit adds support for block scaled tensors.
In particular, the block scaled type has been extended with the
`DenseElementTypeInterface` to allow block scaled data values to be
specified in dense element attributes.
The block scaled type has also been extended to allow optional scale
values to be specified by the type. For now, scale values are not
expected to be propagated beyond their use in the attribute input of a
constant operation. In the future, we may want to propagate these values
to allow certain optimizations.
The `tosa.const` operation has also been updated in the validation pass.
