[SPIRV][OPT] Adding flag to run spirv structurizer (#119301)
This PR adds a new flag into OPT to run SPIRV structurizer, this is
being added improving testing of such pass.
This change is required to implement a test request that come
https://github.com/llvm/llvm-project/pull/116331.
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Co-authored-by: Joao Saffran <jderezende@microsoft.com>