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/mE.cpp

@@ -0,0 +1,45 @@
+#include <cstdlib>
+#include <cstdio>
+#include <iostream>
+
+static void
+bye_setup()
+{
+    std::cout << "mE " << __FUNCTION__ << std::endl;
+}
+
+static void
+bye_func()
+{
+    std::cout << "mE " << __FUNCTION__ << std::endl;
+}
+
+__attribute__((constructor)) void
+setup()
+{
+    std::cout << "mE " << __FUNCTION__ << std::endl;
+    if (std::atexit(bye_setup) != 0) {
+        std::perror("register an atexit handler failed");
+    }
+}
+
+__attribute__((destructor)) void
+teardown()
+{
+    std::cout << "mE " << __FUNCTION__ << std::endl;
+}
+
+__attribute__((export_name("func1"))) void
+func1()
+{
+    std::cout << "mE " << __FUNCTION__ << std::endl;
+    if (std::atexit(bye_func) != 0) {
+        std::perror("register an atexit handler failed");
+    }
+}
+
+__attribute__((export_name("func2"))) void
+func2()
+{
+    std::cout << "mE " << __FUNCTION__ << std::endl;
+}