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
