src: move NAPI_AUTO_LEN from define to static const
This allows tools like rust's bindgen to access this value
Checklist
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make -j4 test(UNIX), orvcbuild test(Windows) passes -
commit message follows commit guidelines
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Do not update/delete: Notification broadcast message test data
This allows tools like rust's bindgen to access this value
make -j4 test (UNIX), or vcbuild test (Windows) passes