[mlir][SVE] Add an e2e test for vector.contract (#69845)

Adds an end-to-end test for `vector.contract` that targets SVE (i.e.
scalable vectors). Note that this requires lifting the restriction on
`vector.outerproduct` (to which `vector.contract` is lowered to) that
would deem the following as invalid by the Op verifier (*):

```
vector.outerproduct %27, %28, %26 {kind = #vector.kind<add>} : vector<3xf32>, vector<[2]xf32>
```

This is indeed valid as the end-to-end test demonstrates (at least when
compiling for SVE).