With the removal of mlir-vulkan-runner (as part of #73457) in
e7e3c45bc70904e24e2b3221ac8521e67eb84668, mlir-cpu-runner is now the
only runner for all CPU and GPU targets, and the "cpu" name has been
misleading for some time already. This commit renames it to mlir-runner.
This follows up on 733be4ed7dcf976719f424c0cb81b77a14f91f5a, which made
mlir-vulkan-runner and its associated passes redundant, and completes
the main goal of #73457. The mlir-vulkan-runner tests become part of the
integration test suite, and the Vulkan runner runtime components become
part of ExecutionEngine, just as was done when removing other
target-specific runners.
