mergestate: move staticmethod _filectxorabsent to module level

I suspect this was a static method just because it made merge.py feel
less messy, but now we have a mergestate package so we can do better.

Differential Revision: https://phab.mercurial-scm.org/D8591

mercurial/mergestate.py

@@ -31,6 +31,13 b' def _droponode(data):'
     return b'\0'.join(bits)
 
 
+def _filectxorabsent(hexnode, ctx, f):
+    if hexnode == nullhex:
+        return filemerge.absentfilectx(ctx, f)
+    else:
+        return ctx[f]
+
+
 # Merge state record types. See ``mergestate`` docs for more.
 RECORD_LOCAL = b'L'
 RECORD_OTHER = b'O'
@@ -600,8 +607,8 b' class mergestate(object):'
             actx = self._repo[anccommitnode]
         else:
             actx = None
-        fcd = self._filectxorabsent(localkey, wctx, dfile)
-        fco = self._filectxorabsent(onode, octx, ofile)
+        fcd = _filectxorabsent(localkey, wctx, dfile)
+        fco = _filectxorabsent(onode, octx, ofile)
         # TODO: move this to filectxorabsent
         fca = self._repo.filectx(afile, fileid=anode, changectx=actx)
         # "premerge" x flags
@@ -679,12 +686,6 b' class mergestate(object):'
 
         return complete, r
 
-    def _filectxorabsent(self, hexnode, ctx, f):
-        if hexnode == nullhex:
-            return filemerge.absentfilectx(ctx, f)
-        else:
-            return ctx[f]
-
     def preresolve(self, dfile, wctx):
         """run premerge process for dfile