Register a -test-spirv-roundtrip hook to mlir-translate

This CL registers a new mlir-translate hook, -test-spirv-roundtrip,
for testing SPIR-V serialization and deserialization round-trip.

This CL also moves the existing -serialize-spirv and
-deserialize-spirv hooks to one source file.

PiperOrigin-RevId: 269659528