project: reorganize the structure of the project.

* 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.

src/Commands/IsLFSFiltered.cs

@@ -0,0 +1,19 @@
+namespace SourceGit.Commands
+{
+    public class IsLFSFiltered : Command
+    {
+        public IsLFSFiltered(string repo, string path)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = $"check-attr -a -z \"{path}\"";
+            RaiseError = false;
+        }
+
+        public bool Result()
+        {
+            var rs = ReadToEnd();
+            return rs.IsSuccess && rs.StdOut.Contains("filter\0lfs");
+        }
+    }
+}