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/QueryStagedFileBlobGuid.cs

@@ -0,0 +1,29 @@
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Commands
+{
+    public partial class QueryStagedFileBlobGuid : Command
+    {
+        [GeneratedRegex(@"^\d+\s+([0-9a-f]+)\s+.*$")]
+        private static partial Regex REG_FORMAT();
+
+        public QueryStagedFileBlobGuid(string repo, string file)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = $"ls-files -s -- \"{file}\"";
+        }
+
+        public string Result()
+        {
+            var rs = ReadToEnd();
+            var match = REG_FORMAT().Match(rs.StdOut.Trim());
+            if (match.Success)
+            {
+                return match.Groups[1].Value;
+            }
+
+            return string.Empty;
+        }
+    }
+}