Update import path for PackageFinder/FormatControl

PackageFinder moved to pip._internal.index.package_finder
FormatControl moved to pip._internal.models.format_control
See: pypa/pip#7144

piptools/_compat/pip_compat.py

@@ -36,8 +36,8 @@ def do_import(module_path, subimport=None, old_path=None):
 FAVORITE_HASH = do_import("utils.hashes", "FAVORITE_HASH")
 path_to_url = do_import("utils.urls", "path_to_url", old_path="download")
 url_to_path = do_import("utils.urls", "url_to_path", old_path="download")
-PackageFinder = do_import("index", "PackageFinder")
-FormatControl = do_import("index", "FormatControl")
+PackageFinder = do_import("index.package_finder", "PackageFinder", old_path="index")
+FormatControl = do_import("models.format_control", "FormatControl", old_path="index")
 InstallCommand = do_import("commands.install", "InstallCommand")
 Wheel = do_import("wheel", "Wheel")
 cmdoptions = do_import("cli.cmdoptions", old_path="cmdoptions")