Affine Loop Fusion Utility Module (1/n).

    *) Adds LoopFusionUtils which will expose a set of loop fusion utilities (e.g. dependence checks, fusion cost/storage reduction, loop fusion transformation) for use by loop fusion algorithms. Support for checking block-level fusion-preventing dependences is added in this CL (additional loop fusion utilities will be added in subsequent CLs).
    *) Adds TestLoopFusion test pass for testing LoopFusionUtils at a fine granularity.
    *) Adds unit test for testing dependence check for block-level fusion-preventing dependences.

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PiperOrigin-RevId: 249861071