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/QueryFileSize.cs

@@ -0,0 +1,38 @@
+using System.Text.RegularExpressions;
+
+namespace SourceGit.Commands
+{
+    public partial class QueryFileSize : Command
+    {
+
+        [GeneratedRegex(@"^\d+\s+\w+\s+[0-9a-f]+\s+(\d+)\s+.*$")]
+        private static partial Regex REG_FORMAT();
+
+        public QueryFileSize(string repo, string file, string revision)
+        {
+            WorkingDirectory = repo;
+            Context = repo;
+            Args = $"ls-tree {revision} -l -- {file}";
+        }
+
+        public long Result()
+        {
+            if (_result != 0)
+                return _result;
+
+            var rs = ReadToEnd();
+            if (rs.IsSuccess)
+            {
+                var match = REG_FORMAT().Match(rs.StdOut);
+                if (match.Success)
+                {
+                    return long.Parse(match.Groups[1].Value);
+                }
+            }
+
+            return 0;
+        }
+
+        private readonly long _result = 0;
+    }
+}