use WIN_StringToUTF8W instead of WIN_StringToUTF8 where needed (#2)

cf. bug #5435.
- SDL_wasapi_win32.c (GetWasapiDeviceName): pwszVal is WCHAR*
- windows/SDL_sysfilesystem.c (SDL_GetBasePath, SDL_GetPrefPath)
- windows/SDL_sysurl.c (SDL_SYS_OpenURL): wurl is WCHAR*
- SDL_windowssensor.c (ConnectSensor): bstr_name is WCHAR*
- windows/SDL_systhread.c (SDL_SYS_SetupThread): strw is WCHAR*

src/misc/windows/SDL_sysurl.c

@@ -37,7 +37,7 @@ SDL_SYS_OpenURL(const char *url)
         return WIN_SetErrorFromHRESULT("CoInitialize failed", hr);
     }
 
-    wurl = WIN_UTF8ToString(url);
+    wurl = WIN_UTF8ToStringW(url);
     if (wurl == NULL) {
         WIN_CoUninitialize();
         return SDL_OutOfMemory();