Restore "delayed" aspect of existing import of pkg_resources in setuptools/installer.py (#4994)

Author: abravalheri

setuptools/installer.py

@@ -6,8 +6,7 @@
 import sys
 import tempfile
 from functools import partial
-
-from pkg_resources import Distribution
+from typing import TYPE_CHECKING
 
 from . import _reqs
 from ._reqs import _StrOrIter
@@ -17,6 +16,9 @@
 from distutils import log
 from distutils.errors import DistutilsError
 
+if TYPE_CHECKING:
+    from pkg_resources import Distribution
+
 
 def _fixup_find_links(find_links):
     """Ensure find-links option end-up being a list of strings."""