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

core/iwasm/common/wasm_runtime_common.c

@@ -2294,13 +2294,13 @@ wasm_runtime_is_wasi_mode(WASMModuleInstanceCommon *module_inst)
 {
 #if WASM_ENABLE_INTERP != 0
     if (module_inst->module_type == Wasm_Module_Bytecode
-        && ((WASMModuleInstance *)module_inst)->module->is_wasi_module)
+        && ((WASMModuleInstance *)module_inst)->module->import_wasi_api)
         return true;
 #endif
 #if WASM_ENABLE_AOT != 0
     if (module_inst->module_type == Wasm_Module_AoT
         && ((AOTModule *)((AOTModuleInstance *)module_inst)->aot_module.ptr)
-               ->is_wasi_module)
+               ->import_wasi_api)
         return true;
 #endif
     return false;