Add WASI ABI compatibility check for multi-module (#913)

Refer to https://github.com/WebAssembly/WASI/blob/main/design/application-abi.md
to check the WASI ABI compatibility:
- Command (main module) may export _start function with signature "()"
- Reactor (sub module) may export _initialize function with signature "()"
- _start and _initialize can not be exported at the same time
- Reactor cannot export _start function
- Command and Reactor must export memory

And
- Rename module->is_wasi_module to module->import_wasi_api
- Refactor wasm_loader_find_export()
- Remove MULTI_MODULE related codes from mini_loader
- Update multi-module samples
- Fix a "use-after-free" issue. Since we reuse the memory instance of sub module,
   just to protect it from freeing an imported memory instance

samples/multi-module/wasm-apps/mD.cpp

@@ -0,0 +1,74 @@
+#include <cstdlib>
+#include <cstdio>
+#include <iostream>
+
+static void
+bye_main()
+{
+    std::cout << "mD " << __FUNCTION__ << std::endl;
+}
+
+static void
+bye_setup()
+{
+    std::cout << "mD " << __FUNCTION__ << std::endl;
+}
+
+static void
+bye_func()
+{
+    std::cout << "mD " << __FUNCTION__ << std::endl;
+}
+
+void
+func3() __attribute__((__import_module__("mE"), __import_name__("func1")));
+
+void
+func4() __attribute__((__import_module__("mE"), __import_name__("func2")));
+
+void
+func1()
+{
+    std::printf("mD %s\n", __FUNCTION__);
+    if (std::atexit(bye_func) != 0) {
+        std::perror("register an atexit handler failed");
+    }
+    func3();
+}
+
+void
+func2()
+{
+    std::printf("mD %s\n", __FUNCTION__);
+    func4();
+}
+
+__attribute__((constructor)) void
+setup()
+{
+    std::cout << "mD " << __FUNCTION__ << std::endl;
+    if (std::atexit(bye_setup) != 0) {
+        std::perror("register an atexit handler failed");
+    }
+}
+
+__attribute__((destructor)) void
+teardown()
+{
+    std::cout << "mD " << __FUNCTION__ << std::endl;
+}
+
+int
+main()
+{
+    std::printf("mD %s\n", __FUNCTION__);
+
+    if (std::atexit(bye_main) != 0) {
+        std::perror("register an atexit handler failed");
+        return EXIT_FAILURE;
+    }
+
+    func1();
+    func2();
+    return EXIT_SUCCESS;
+}