Exit application method is replaced by 'ui_app_exit' (#3)

The function 'exit(EXIT_SUCCESS)' terminates the calling process
immediately. The better way to exit process is to call 'ui_app_exit'
which invokes the terminate callback on main thread so that the
app can save its current status before exiting.

shell/platform/tizen/BUILD.gn

@@ -63,6 +63,7 @@ source_set("flutter_tizen") {
 
   include_dirs = [
     "//third_party/tizen_tools/sysroot/$target_cpu/usr/include",
+    "//third_party/tizen_tools/sysroot/$target_cpu/usr/include/appfw",
     "//third_party/tizen_tools/sysroot/$target_cpu/usr/include/base",
     "//third_party/tizen_tools/sysroot/$target_cpu/usr/include/dlog",
     "//third_party/tizen_tools/sysroot/$target_cpu/usr/include/ecore-1",
@@ -89,6 +90,7 @@ source_set("flutter_tizen") {
 
   libs = [
     "base-utils-i18n",
+    "capi-appfw-application",
     "capi-system-info",
     "capi-system-system-settings",
     "dlog",

shell/platform/tizen/channels/platform_channel.cc

@@ -4,6 +4,8 @@
 
 #include "platform_channel.h"
 
+#include <app.h>
+
 #include "flutter/shell/platform/common/cpp/json_method_codec.h"
 #include "flutter/shell/platform/tizen/logger.h"
 
@@ -28,7 +30,7 @@ void PlatformChannel::HandleMethodCall(
   const auto method = call.method_name();
 
   if (method == "SystemNavigator.pop") {
-    exit(EXIT_SUCCESS);
+    ui_app_exit();
     result->Success();
   } else if (method == "SystemSound.play") {
     result->NotImplemented();