[mlir][spirv] Add an argmax integration test with `mlir-vulkan-runner` (#106426)
This PR adds an integration test for an argmax kernel with
`mlir-vulkan-runner`. This test exercises the `convert-to-spirv` pass
(landed in #95942) and demonstrates that we can use SPIR-V ops as
"intrinsics" among higher-level dialects.
The support for `index` dialect in `mlir-vulkan-runner` is also added.