Convert coerce_to_int32s and bitwise_op to take operand temps as
explicit parameters, then migrate UnaryPlus.
The bitwise_op macro is the actual body of BitwiseAnd, BitwiseOr, and
BitwiseXor (which just call into it), so a single macro migration
covers all three handlers. UnaryPlus is migrated alongside since it
shares the same coerce-to-int32 conceptual path.
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