init: Add --use-local-gitdirs for standard Git layouts

Introduce --use-local-gitdirs to bypass repo's symlink-based layouts in
favor of standard local .git directories.

Bug: 513329573
Bug: 508146070
Change-Id: I53d1602e61be0b86964529bcbea3dc801471f9c9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/569001
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Reviewed-by: Dan Willemsen <dwillemsen@google.com>

subcmds/init.py

@@ -169,6 +169,7 @@ to update the working directory files.
             depth=opt.depth,
             git_event_log=self.git_event_log,
             manifest_name=opt.manifest_name,
+            use_local_gitdirs=opt.use_local_gitdirs,
         ):
             manifest_name = opt.manifest_name
             raise UpdateManifestError(