Fixes #5200 - Prevent FileDialog Enter navigation from selecting the first file

[Copilot]

Proposed Changes/Todos

The file dialog was rewriting Path to the first row in the newly opened directory when Enter was used from the table, which made folder navigation behave like an implicit file selection. This change keeps Enter-driven directory navigation on the opened directory so the file list is shown without auto-selecting the first file.

• Regression coverage
  • Added a focused FileDialogResultTests case for Enter on a directory row in the table.
• State transition fix
  • Suppressed TableViewOnValueChanged (...) path synchronization while FileDialog is internally pushing a new directory state.
  • This prevents the internal reset to row 0 from overwriting the just-opened directory path.
• Behavior after Enter navigation
  • Path remains on the opened directory.
  • The new directory contents are displayed and available for selection.

if (_pushingState || !_tableView.HasFocus || _tableView.Value is null || _tableView.Table?.Rows == 0)
{
    return;
}

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[Copilot]

Pull request overview

This PR fixes an unintended FileDialog behavior where pressing Enter on a directory row in the file list could rewrite Path to the first row of the newly opened directory (making directory navigation behave like an implicit file selection). The change prevents TableViewOnValueChanged from synchronizing Path while FileDialog is internally pushing a new directory state.

Changes:

• Suppress TableViewOnValueChanged path synchronization when _pushingState is true to avoid overwriting the just-opened directory path during internal navigation.
• Add a regression unit test verifying that Enter-accepting a directory from the table keeps Path on the opened directory after navigation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Tests/UnitTestsParallelizable/Views/FileDialogResultTests.cs	Adds a regression test covering Enter navigation into a directory from the table view.
Terminal.Gui/Views/FileDialogs/FileDialog.TableView.cs	Guards TableViewOnValueChanged with _pushingState to prevent path rewrites during internal state transitions.

[tig]

This needs @tznind's approval since he reported it.