typing: make the filelog class known to pytype

These are the same changes as c1d7ac70980b and 45270e286bdc made to dirstate,
for the same reasons.

mercurial/filelog.py

@@ -6,6 +6,8
 # GNU General Public License version 2 or any later version.
 
 
+import typing
+
 from .i18n import _
 from .node import nullrev
 from . import (
@@ -23,8 +25,7 from .revlogutils import (
 )
 
 
[e-mail](repository.ifilestorage)
-class filelog:
+class FileLog:
     def __init__(self, opener, path, try_split=False):
         self._revlog = revlog.revlog(
             opener,
@@ -262,6 +263,12 class filelog:
         return self._revlog.clone(tr, destrevlog._revlog, **kwargs)
 
 
+filelog = interfaceutil.implementer(repository.ifilestorage)(FileLog)
+
+if typing.TYPE_CHECKING:
+    filelog = FileLog
+
+
 class narrowfilelog(filelog):
     """Filelog variation to be used with narrow stores."""