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/FileHistories.cs

@@ -0,0 +1,84 @@
+using System.Collections.Generic;
+using System.Threading.Tasks;
+
+using Avalonia.Threading;
+
+using CommunityToolkit.Mvvm.ComponentModel;
+
+namespace SourceGit.ViewModels
+{
+    public class FileHistories : ObservableObject
+    {
+        public bool IsLoading
+        {
+            get => _isLoading;
+            private set => SetProperty(ref _isLoading, value);
+        }
+
+        public List<Models.Commit> Commits
+        {
+            get => _commits;
+            set => SetProperty(ref _commits, value);
+        }
+
+        public Models.Commit SelectedCommit
+        {
+            get => _selectedCommit;
+            set
+            {
+                if (SetProperty(ref _selectedCommit, value))
+                {
+                    if (value == null)
+                    {
+                        DiffContext = null;
+                        DetailContext.Commit = null;
+                    }
+                    else
+                    {
+                        DiffContext = new DiffContext(_repo, new Models.DiffOption(value, _file), _diffContext);
+                        DetailContext.Commit = value;
+                    }
+                }
+            }
+        }
+
+        public DiffContext DiffContext
+        {
+            get => _diffContext;
+            set => SetProperty(ref _diffContext, value);
+        }
+
+        public CommitDetail DetailContext
+        {
+            get => _detailContext;
+            set => SetProperty(ref _detailContext, value);
+        }
+
+        public FileHistories(string repo, string file)
+        {
+            _repo = repo;
+            _file = file;
+            _detailContext = new CommitDetail(repo);
+
+            Task.Run(() =>
+            {
+                var commits = new Commands.QueryCommits(_repo, $"-n 10000 -- \"{file}\"").Result();
+                Dispatcher.UIThread.Invoke(() =>
+                {
+                    IsLoading = false;
+                    Commits = commits;
+                    if (commits.Count > 0)
+                        SelectedCommit = commits[0];
+                });
+            });
+        }
+
+        private readonly string _repo = string.Empty;
+        private readonly string _file = string.Empty;
+        private bool _isLoading = true;
+        private List<Models.Commit> _commits = null;
+        private Models.Commit _selectedCommit = null;
+        private DiffContext _diffContext = null;
+        private CommitDetail _detailContext = null;
+    }
+}