it should be byte size, not the number of (fp32) values.
i'm ambivalent about how to deal with the compatibility for
the legacy wamr-specific "wasi_nn". for now, i avoided changing it.
(so that existing tests using the legacy abi, namely test_tensorflow.c
and test_tensorflow_quantized.c, passes as they are.)
if we have any users who still want to use the legacy abi,
i suppose they consider the compatibility is more important
than the consistency with other backends.
cf. https://github.com/bytecodealliance/wasm-micro-runtime/issues/4376
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