histedit: create state and acquire locks earlier
This makes chistedit (histedit with curses UI) not write any files inside repo
without wlock. It also makes sense to wrap the entire process of preparing
commands inside the curses UI inside locks because we don't want anything else
to touch wdir or repo during this time.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).