Fixes#726. Looks like a980cc987d isn't sufficient. It sorts the commits according to the ordering in history, but then CherryPick ViewModel reverses the order.
This commit changes CherryPick ViewModel to use string.Join on the commit list without reordering, so that the ordering is controlled entirely by the caller.
* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.
