feat: added AvaloniaEdit for the text editor with basic highlight an line count, better "about" dialog and adde textmate

GsaEditor/Views/MainWindow.axaml

@@ -3,6 +3,7 @@
         xmlns:vm="using:GsaEditor.ViewModels"
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+        xmlns:aedit="https://github.com/avaloniaui/avaloniaedit"
         mc:Ignorable="d" d:DesignWidth="1100" d:DesignHeight="700"
         x:Class="GsaEditor.Views.MainWindow"
         x:CompileBindings="False"
@@ -199,13 +200,12 @@
                             <Button Content="Cancel" Command="{Binding CancelEditCommand}"
                                     IsVisible="{Binding IsEditingText}"/>
                         </StackPanel>
-                        <TextBox Text="{Binding PreviewText, Mode=TwoWay}"
-                                 IsReadOnly="{Binding !IsEditingText}"
-                                 FontFamily="Consolas, Courier New, monospace"
-                                 FontSize="13"
-                                 AcceptsReturn="True"
-                                 TextWrapping="NoWrap"
-                                 Margin="10,0,10,10"/>
+                        <aedit:TextEditor Name="TextEditor"
+                                          IsReadOnly="{Binding !IsEditingText}"
+                                          FontFamily="Consolas, Courier New, monospace"
+                                          FontSize="13"
+                                          ShowLineNumbers="True"
+                                          Margin="10,0,10,10"/>
                     </DockPanel>
 
                     <!-- Image Preview -->