histedit: add a stateobj variable to histeditstate class

The stateobj variable will be an instance of state.cmdstate() class. The
stateobj variable will be used in upcoming patches to simplify the code a bit
and start using cbor to write state files.

Differential Revision: https://phab.mercurial-scm.org/D3864

hgext/histedit.py

@@ -207,6 +207,7 b' from mercurial import ('
     registrar,
     repair,
     scmutil,
+    state as statemod,
     util,
 )
 from mercurial.utils import (
@@ -304,6 +305,7 b' class histeditstate(object):'
         self.lock = lock
         self.wlock = wlock
         self.backupfile = None
+        self.stateobj = statemod.cmdstate(repo, 'histedit-state')
         if replacements is None:
             self.replacements = []
         else: