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/utils.h

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2019 Intel Corporation.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef WASI_NN_UTILS
+#define WASI_NN_UTILS
+
+#include <stdint.h>
+
+#include "wasi_nn.h"
+
+#define MAX_MODEL_SIZE 85000000
+#define MAX_OUTPUT_TENSOR_SIZE 200
+#define INPUT_TENSOR_DIMS 4
+#define EPSILON 1e-8
+
+typedef struct {
+    float *input_tensor;
+    uint32_t *dim;
+    uint32_t elements;
+} input_info;
+
+/* wasi-nn wrappers */
+
+error
+wasm_load(char *model_name, graph *g, execution_target target);
+
+error
+wasm_init_execution_context(graph g, graph_execution_context *ctx);
+
+error
+wasm_set_input(graph_execution_context ctx, float *input_tensor, uint32_t *dim);
+
+error
+wasm_compute(graph_execution_context ctx);
+
+error
+wasm_get_output(graph_execution_context ctx, uint32_t index, float *out_tensor,
+                uint32_t *out_size);
+
+/* Utils */
+
+float *
+run_inference(execution_target target, float *input, uint32_t *input_size,
+              uint32_t *output_size, char *model_name,
+              uint32_t num_output_tensors);
+
+input_info
+create_input(int *dims);
+
+#endif