Implement module instance context APIs (#2436)

Introduce module instance context APIs which can set one or more contexts created
by the embedder for a wasm module instance:
```C
    wasm_runtime_create_context_key
    wasm_runtime_destroy_context_key
    wasm_runtime_set_context
    wasm_runtime_set_context_spread
    wasm_runtime_get_context
```

And make libc-wasi use it and set wasi context as the first context bound to the wasm
module instance.

Also add samples.

Refer to https://github.com/bytecodealliance/wasm-micro-runtime/issues/2460.

core/iwasm/common/wasm_runtime_common.h

@@ -939,6 +939,26 @@ WASM_RUNTIME_API_EXTERN bool
 wasm_runtime_unregister_natives(const char *module_name,
                                 NativeSymbol *native_symbols);
 
+/* See wasm_export.h for description */
+WASM_RUNTIME_API_EXTERN void *
+wasm_runtime_create_context_key(void (*dtor)(WASMModuleInstanceCommon *inst,
+                                             void *ctx));
+
+/* See wasm_export.h for description */
+WASM_RUNTIME_API_EXTERN void
+wasm_runtime_destroy_context_key(void *key);
+
+/* See wasm_export.h for description */
+WASM_RUNTIME_API_EXTERN void
+wasm_runtime_set_context(WASMModuleInstanceCommon *inst, void *key, void *ctx);
+/* See wasm_export.h for description */
+WASM_RUNTIME_API_EXTERN void
+wasm_runtime_set_context_spread(WASMModuleInstanceCommon *inst, void *key,
+                                void *ctx);
+/* See wasm_export.h for description */
+WASM_RUNTIME_API_EXTERN void *
+wasm_runtime_get_context(WASMModuleInstanceCommon *inst, void *key);
+
 bool
 wasm_runtime_invoke_native(WASMExecEnv *exec_env, void *func_ptr,
                            const WASMType *func_type, const char *signature,