upgrade: implement partial upgrade for upgrading persistent-nodemap Upgrading repositories to use persistent nodemap should be fast and easy as it requires only two things: 1) Updating the requirements 2) Writing a persistent-nodemap on disk For both of the steps above, we don't need to edit existing revlogs. This patch makes upgrade only do the above mentioned two steps if we are only upgarding to use persistent-nodemap feature. Since `nodemap.persist_nodemap()` assumes that there exists a nodemap file for the given revlog if we are trying to call it, this patch adds `force` argument to create a file if does not exist which is true in our upgrade case. The test changes demonstrate that we no longer write nodemap files for manifest after upgrade which I think is desirable. Differential Revision: https://phab.mercurial-scm.org/D9936