Support git repositories which use the sparse checkout git feature

Hello!
Git introduced a new feature called sparse-checkout This command is very useful in large repositories containing a lot of projects. Using sparse-checkout and partial repository clone allow substantially reduce occupied by the repository space on local disk.

GitDiffMargin is a useful extension for Visual Studio, This extension uses the libgit2sharp. The extension is not work with repositories uses sparse-checkout because such repositories are not supported.

Reproduction steps

Git Diff Margin get an exception unsupported repository version 1. Only versions up to 0 are supported. while creating a Repository on this line.

Refer to the according GitDiffMargin issue for more info:https://github.com/laurentkempe/GitDiffMargin/issues/356

GitDiffMargin/Git/GitCommands.cs の 43 行目とリンク先の GitDiffMargin issue から始め、Git と libgit2sharp によって sparse-checkout リポジトリがどのように表現されるかを確認します。sparse-checkout リポジトリでリポジトリバージョン例外を再現し、そのようなリポジトリを開いても失敗しなくなっていることを検証します。