Refine full save backup helper API

Narrow the backup save helper to full game saves only.

Replace pfile_write_hero_with_backup(bool writeGameData) with
pfile_write_game_with_backup(), and always write full game data
before validating the resulting archive with ArchiveContainsGame().

This makes the helper's name, behavior, and post-write validation
consistent, and removes an API parameter that made the function look
more general than its actual responsibility.

Also update SaveGame() to use the new helper name and a clearer local
variable.

Source/loadsave.cpp

@@ -2934,8 +2934,8 @@ void SaveGame()
 	pfile_write_hero(/*writeGameData=*/true);
 	sfile_write_stash();
 #else
-	const bool heroSaved = pfile_write_hero_with_backup(/*writeGameData=*/true);
-	if (!heroSaved) {
+	const bool gameSaved = pfile_write_game_with_backup();
+	if (!gameSaved) {
 		gbValidSaveFile = false;
 		return;
 	}

Source/pfile.cpp

@@ -644,7 +644,7 @@ void pfile_write_hero(bool writeGameData)
 }
 
 #if !(defined(UNPACKED_SAVES) && defined(DVL_NO_FILESYSTEM))
-bool pfile_write_hero_with_backup(bool writeGameData)
+bool pfile_write_game_with_backup()
 {
 	const std::string backupPrefix = "backup_";
 	const std::string backupLocation = GetSavePath(gSaveNumber, backupPrefix);
@@ -653,7 +653,7 @@ bool pfile_write_hero_with_backup(bool writeGameData)
 	if (FileExists(saveLocation) || DirectoryExists(saveLocation.c_str()))
 		CopySaveLocation(saveLocation, backupLocation);
 
-	pfile_write_hero(writeGameData);
+	pfile_write_hero(/*writeGameData=*/true);
 
 	auto archive = OpenSaveArchive(gSaveNumber);
 	const bool saveIsValid = archive && ArchiveContainsGame(*archive);

Source/pfile.h

@@ -100,8 +100,8 @@ std::optional<SaveReader> OpenSaveArchive(uint32_t saveNum);
 std::optional<SaveReader> OpenStashArchive();
 const char *pfile_get_password();
 std::unique_ptr<std::byte[]> ReadArchive(SaveReader &archive, const char *pszName, size_t *pdwLen = nullptr);
-void pfile_write_hero(bool writeGameData = false);
-bool pfile_write_hero_with_backup(bool writeGameData = false);
+void pfile_write_hero(bool writeGameData = false);
+bool pfile_write_game_with_backup();
 bool pfile_write_stash_with_backup();
 
 #ifndef DISABLE_DEMOMODE