Fix json invalid utf-8 from IconPath (#13340)

When storing the IconPath value directly as a string we are subject
to unspecified behaviour as Windows stores paths as 16-bit wchar_t and
std::string doesn't convey a specific char encoding.

To be specific we need to access the icon path in its native format
(which we assume to be std::wstring) and convert it to multibyte.

src/windows/service/exe/LxssUserSession.cpp

@@ -2683,7 +2683,7 @@ try
 
         e["name"] = WideToMultiByte(Configuration.Name);
         e["guid"] = WideToMultiByte(distributionProfileId);
-        e["icon"] = IconPath.string();
+        e["icon"] = WideToMultiByte(IconPath.native());
 
         // See https://github.com/microsoft/terminal/pull/18195. Supported in terminal >= 1.23
         e["pathTranslationStyle"] = "wsl";