Extract parser setup to helper function

- Allows users who `import` the scripts to examine the parser programmatically

train_textual_inversion.py

@@ -526,7 +526,7 @@ def load_weights(file):
     return emb
 
 
-if __name__ == "__main__":
+def setup_parser() -> argparse.ArgumentParser:
     parser = argparse.ArgumentParser()
 
     train_util.add_sd_models_arguments(parser)
@@ -565,6 +565,12 @@ if __name__ == "__main__":
         help="ignore caption and use default templates for stype / キャプションは使わずデフォルトのスタイル用テンプレートで学習する",
     )
 
+    return parser
+
+
+if __name__ == "__main__":
+    parser = setup_parser()
+
     args = parser.parse_args()
     args = train_util.read_config_from_file(args, parser)