typing: consolidate "if not globals():" trick

Removes redundant inline comments. I think pycompat is good place to host
this kind of constants.

mercurial/branchmap.py

@@ -27,7 +27,7 b' from .utils import ('
     stringutil,
 )
 
-if not globals():
+if pycompat.TYPE_CHECKING:
     from typing import (
         Any,
         Callable,

mercurial/cmdutil.py

@@ -61,7 +61,7 b' from .utils import ('
     stringutil,
 )
 
-if not globals():
+if pycompat.TYPE_CHECKING:
     from typing import (
         Any,
         Dict,

mercurial/encoding.py

@@ -20,14 +20,11 b' from . import ('
 
 from .pure import charencode as charencodepure
 
-_TYPE_CHECKING = False
-
-if not globals():  # hide this from non-pytype users
+if pycompat.TYPE_CHECKING:
     from typing import (
         Any,
         Callable,
         List,
-        TYPE_CHECKING as _TYPE_CHECKING,
         Text,
         Type,
         TypeVar,
@@ -124,7 +121,7 b' class localstr(bytes):'
         s._utf8 = u
         return s
 
-    if _TYPE_CHECKING:
+    if pycompat.TYPE_CHECKING:
         # pseudo implementation to help pytype see localstr() constructor
         def __init__(self, u, l):
             # type: (bytes, bytes) -> None

mercurial/logcmdutil.py

@@ -42,7 +42,7 b' from .utils import ('
 )
 
 
-if not globals():
+if pycompat.TYPE_CHECKING:
     from typing import (
         Any,
         Tuple,

mercurial/mail.py

@@ -36,7 +36,7 b' from .utils import ('
     stringutil,
 )
 
-if not globals():  # hide this from non-pytype users
+if pycompat.TYPE_CHECKING:
     from typing import Any, List, Tuple, Union
 
     # keep pyflakes happy

mercurial/pycompat.py

@@ -20,6 +20,12 b' import tempfile'
 
 ispy3 = sys.version_info[0] >= 3
 ispypy = '__pypy__' in sys.builtin_module_names
+TYPE_CHECKING = False
+
+if not globals():  # hide this from non-pytype users
+    import typing
+
+    TYPE_CHECKING = typing.TYPE_CHECKING
 
 if not ispy3:
     import cookielib

mercurial/state.py

@@ -23,11 +23,12 b' from .i18n import _'
 
 from . import (
     error,
+    pycompat,
     util,
 )
 from .utils import cborutil
 
-if not globals():
+if pycompat.TYPE_CHECKING:
     from typing import (
         Any,
         Dict,