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/ViewModels/TwoSideTextDiff.cs

@@ -0,0 +1,56 @@
+using System.Collections.Generic;
+
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace SourceGit.ViewModels
+{
+    public class TwoSideTextDiff : ObservableObject
+    {
+        public string File { get; set; } = string.Empty;
+        public List<Models.TextDiffLine> Old { get; set; } = new List<Models.TextDiffLine>();
+        public List<Models.TextDiffLine> New { get; set; } = new List<Models.TextDiffLine>();
+        public int MaxLineNumber = 0;
+
+        public TwoSideTextDiff(Models.TextDiff diff)
+        {
+            File = diff.File;
+            MaxLineNumber = diff.MaxLineNumber;
+
+            foreach (var line in diff.Lines)
+            {
+                switch (line.Type)
+                {
+                    case Models.TextDiffLineType.Added:
+                        New.Add(line);
+                        break;
+                    case Models.TextDiffLineType.Deleted:
+                        Old.Add(line);
+                        break;
+                    default:
+                        FillEmptyLines();
+                        Old.Add(line);
+                        New.Add(line);
+                        break;
+                }
+            }
+
+            FillEmptyLines();
+        }
+
+        private void FillEmptyLines()
+        {
+            if (Old.Count < New.Count)
+            {
+                int diff = New.Count - Old.Count;
+                for (int i = 0; i < diff; i++)
+                    Old.Add(new Models.TextDiffLine());
+            }
+            else if (Old.Count > New.Count)
+            {
+                int diff = Old.Count - New.Count;
+                for (int i = 0; i < diff; i++)
+                    New.Add(new Models.TextDiffLine());
+            }
+        }
+    }
+}