* use system chrome instead of custom caption button on macOS
* move `BeginMoveWindow` and `MaximizeOrRestoreWindow` to `ChromelessWindow`
* better supports for fullscreen mode on macOS
* redesign the layout of title bar for all windows
Signed-off-by: leo <longshuang@msn.cn>
* input font name directly instead of a font picker because localized font family name is not supported by Avalonia
* fallback monospace font to default font
* remove unused code
* 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.
