[mlir][vector] Add support for scalable vectors to VectorLinearize (#86786)

Adds support for scalable vectors to patterns defined in
VectorLineralize.cpp.

Linearization is disable in 2 notable cases:
  * vectors with more than 1 scalable dimension (we cannot represent
    vscale^2),
  * vectors initialised with arith.constant that's not a vector splat
    (such arith.constant Ops cannot be flattened).