**Description**
This PR adds a new option for `convert-to-spirv` pass to clone and
convert only GPU kernel modules for integration testing. The reason for
using pass options instead of two separate passes is that they both
consist of `memref` types conversion and individual dialect patterns,
except they run on different scopes. The PR also replaces the
`gpu-to-spirv` pass with the `convert-to-spirv` pass (with the new
option) in `mlir-vulkan-runner`.
**Future Plan**
Use nesting pass pipelines in `mlir-vulkan-runner` instead of adding
this option.
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Co-authored-by: Jakub Kuderski <kubakuderski@gmail.com>
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