Use FileCheck to test SDBM

    SDBM has an output format representing the unterlying matrix and stripe
    expressions.  Move the SDBM tests from unit testing framework to
    FileCheck-based tests, printing them to the standard output and using FileCheck
    to test the output.  Tests that check the API proper (e.g. that SDBM
    expressions have a specific subtype) and that rely on non-syntatic properties
    (equality of the set of constraints) are not ported.

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PiperOrigin-RevId: 249006055