records.ss mixed the record/protocol/reify model with JVM exception emulation.
Move the contiguous ex-info accessors, the exception supertype hierarchy,
instance-check, case-string, and the instance-check def-var into records-interop.ss,
loaded right after records.ss. Those are only called at runtime, so the relocated
forms resolve fine; records.ss is now the value model and protocol dispatch.
Runtime shim — no seed change.
