fix(vcs): Keep submodule entries out of Rollback and refresh the log of another repository

- Rollback no longer offers a submodule's own entry: it cannot be reverted from the
  enclosing repository (it did nothing while reporting "Rolled back 1 file"). Rolling
  back only that entry explains how to revert it instead.
- A selected change is rolled back alone; only folders take the changes below them, so
  selecting a submodule's entry no longer pulls in the uncommitted files inside it.
- The Git log loads the branches of the newly selected repository, so it reloads when
  that repository's refs move (a new branch showed up only after a manual refresh).

src/platform/locales/text/zh.json

@@ -1945,6 +1945,7 @@
   "Structure unavailable": "结构不可用",
   "Subject line length": "主题行长度",
   "Submit": "提交",
+  "Submodule changes cannot be rolled back here": "子模块的变更无法在此回滚",
   "Subpixel": "子像素",
   "Suggested names": "建议的名称",
   "Super Method": "超方法",