feat(submodule): add deinit method to Submodule (#2014)

Mirrors the pattern of `Submodule.add`, `Submodule.update`, and
`Submodule.remove` by exposing `git submodule deinit` as a first-class
method, so callers no longer need the `repo.git.submodule('deinit', ...)`
workaround noted in the issue.

The method delegates to `git submodule deinit [--force] -- <path>` via
`self.repo.git.submodule`, decorated with `@unbare_repo` to match the
other mutating Submodule methods. It unregisters the submodule from
`.git/config` and clears the working-tree directory while leaving
`.gitmodules` and `.git/modules/<name>` intact, so a later `update()`
can re-initialize.

Closes #2014.

Author: mvanhorn

git/objects/submodule/base.py

@@ -49,6 +49,7 @@
     Callable,
     Dict,
     Iterator,
+    List,
     Mapping,
     Sequence,
     TYPE_CHECKING,
@@ -1267,6 +1268,36 @@ def remove(
 
         return self
 
+    @unbare_repo
+    def deinit(self, force: bool = False) -> "Submodule":
+        """Run ``git submodule deinit`` on this submodule.
+
+        This is a thin wrapper around ``git submodule deinit <path>``, paralleling
+        :meth:`add`, :meth:`update`, and :meth:`remove`. It unregisters the
+        submodule (removes its entry from ``.git/config`` and empties the
+        working-tree directory) without deleting the submodule from
+        ``.gitmodules`` or its checked-out repository under ``.git/modules/``.
+        A subsequent :meth:`update` will re-initialize the submodule from the
+        retained contents.
+
+        :param force:
+            If ``True``, pass ``--force`` to ``git submodule deinit``. This
+            allows deinitialization even when the submodule's working tree has
+            local modifications that would otherwise block the command.
+
+        :return:
+            self
+
+        :note:
+            Doesn't work in bare repositories.
+        """
+        args: List[str] = []
+        if force:
+            args.append("--force")
+        args.extend(["--", self.path])
+        self.repo.git.submodule("deinit", *args)
+        return self
+
     def set_parent_commit(self, commit: Union[Commit_ish, str, None], check: bool = True) -> "Submodule":
         """Set this instance to use the given commit whose tree is supposed to
         contain the ``.gitmodules`` blob.