deprecate legacy WAMR-specific "wasi_nn" module (#4382)

wasi_nn.h: deprecate legacy "wasi_nn"

cf. https://github.com/bytecodealliance/wasm-micro-runtime/issues/4326

doc/build_wamr.md

@@ -102,6 +102,7 @@ cmake -DWAMR_BUILD_PLATFORM=linux -DWAMR_BUILD_TARGET=ARM
 
 ### **Enable lib wasi-nn**
 - **WAMR_BUILD_WASI_NN**=1/0, default to disable if not set
+> Note: WAMR_BUILD_WASI_NN without WAMR_BUILD_WASI_EPHEMERAL_NN is deprecated and will likely be removed in future versions of WAMR. Please consider to enable WAMR_BUILD_WASI_EPHEMERAL_NN as well.
 > Note: See [WASI-NN](../core/iwasm/libraries/wasi-nn) for more details.
 
 ### **Enable lib wasi-nn GPU mode**
@@ -360,4 +361,4 @@ For Valgrind, begin with the following configurations and add additional ones as
   -DWAMR_DISABLE_HW_BOUND_CHECK=0 \
   -DWAMR_DISABLE_WRITE_GS_BASE=0
   #...
-```
+```