wasi-nn: Support multiple TFLite models (#2002)

Remove restrictions:
- Only 1 WASM app at a time
- Only 1 model at a time
   - `graph` and `graph-execution-context` are ignored

Refer to previous document:
e8d718096d/core/iwasm/libraries/wasi-nn/README.md

core/iwasm/libraries/wasi-nn/test/build.sh

@@ -7,8 +7,9 @@
     -Wl,--allow-undefined \
     -Wl,--strip-all,--no-entry \
     --sysroot=/opt/wasi-sdk/share/wasi-sysroot \
-    -I.. \
-    -o test_tensorflow.wasm test_tensorflow.c
+    -I.. -I../src/utils \
+    -o test_tensorflow.wasm \
+    test_tensorflow.c utils.c
 
 # TFLite models to use in the tests