SubmoduleCollection.Add() using clone

[JasonGoemaat]

I see two other pull requests for the same feature (#482 and #684) that haven't been updated in 18 months, so I thought I would give it a try since I need this functionality for a project to convert from another source control system.

SubmoduleCollection.Add(url, subdir) acts like the command line 'git submodule add url subdir'.
It calls git_submodule_add_setup, then deletes the directory created by that and clones
into the same directory and calls git_submodule_add_finalize. The end result is that the
.gitmodules file and the 'file' for the submodule directory are staged and ready to commit.

[carlosmn]

This functionality should not live in SubmoduleCollection. It'd be a good candidate for Commands.SubmoduleAdd or Commands.Submdoule.Add where it would be appropriate to emulate a high-level git command.

[jnnwnk]

Did this ever get into a release?
I'm looking exactly for something line this

SubmoduleCollection.Add(url, subdir) acts like the command line 'git submodule add url subdir'.
It calls git_submodule_add_setup, then deletes the directory created by that and clones into the same directory and calls git_submodule_add_finalize. The end result is that the .gitmodules file and the 'file' for the submodule directory are staged and ready to commit.

There is no Submodules.Add(). I can't figure out if this is placed somewhere else like mentioned in the last comment.