Bugfix: Column width regression (since C#14 refactor & cleanup)

[DanielTrommel]

Description:

Using the latest version, I noticed that vertical grid lines (header <> rows) are mis-aligned when (tab-based) navigating away and later returning back to a TableView, which has columns for which I did not specify Widths.

TableView-GridLinesIssue.mp4

Steps to Reproduce:

1. In the SampleApp project:

   1. in method ExampleModelColumnsHelper.OnAutoGeneratingColumns() comment out all lines that set the column widths, e.g.:

           //e.Column.Width = new GridLength(60);
      

   2. In GridLinesPage.xaml replace lines 19-21 (the tableview component) with this code:

          <TabView>
              <TabViewItem Header="TableView">
                  <tv:TableView x:Name="tableView"
                                ItemsSource="{Binding Items}"
                                AutoGeneratingColumn="{x:Bind local:ExampleModelColumnsHelper.OnAutoGeneratingColumns}" />
              </TabViewItem>
              <TabViewItem Header="Tabpage for reproduction test">Some text; navigate to here, and back to see if grid lines are still okay</TabViewItem>
          </TabView>
      

2. Switch the TableView lib project to commit bf62080 or newer

3. Run the application, and go to the Gridlines example; switch to the "reproduction" tab, and back to the tab with the TableView, and you should see mis-aligned columns

Expected behavior:

Grid lines should always align, ideally with auto-resizing for columns for which no Width was provided.

Contribution:

• Narrowed it down to the changes in commit bf62080 (refactor for C# 14);
• The timer logic was removed, and with it the auto calc of the column widths after DesiredWidth updates; restored that code
• In addition CalculateHeaderWidths() is now also triggered from the OnLoaded, which solves my specific problem (switching away and back to the tab with the TableView)

TableView-GridLines-AutoResize.mp4