The `select` and typed `select` Wasm operators create new SSA values in
Cranelift but were not calling `declare_value_needs_stack_map` on the result
when the operand type is a GC reference. This meant the result, when kept on the
Wasm operand stack (not stored in a local variable), would not appear in stack
maps at subsequent safepoints.

If a GC collection occurred at such a safepoint, the collector would not see the
`select`'s result as a live GC root and could free the referenced object,
leading to use-after-free.

The fix checks `select`'s operand types for reference types and declares the
result as requiring inclusion in stack maps when needed.

Merged via the queue into bytecodealliance:main with commit 2cd4882

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fitzgen deleted the select-declare-needs-stack-map branch