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/audio/wasapi/SDL_wasapi_win32.c

@@ -79,7 +79,7 @@ GetWasapiDeviceName(IMMDevice *device)
         PROPVARIANT var;
         PropVariantInit(&var);
         if (SUCCEEDED(IPropertyStore_GetValue(props, &SDL_PKEY_Device_FriendlyName, &var))) {
-            utf8dev = WIN_StringToUTF8(var.pwszVal);
+            utf8dev = WIN_StringToUTF8W(var.pwszVal);
         }
         PropVariantClear(&var);
         IPropertyStore_Release(props);