Fixes #4023 - Changes CommandEventArgs to be based on HandledEventArgs instead of CancelEventArgs

[tig]

Fixes

• Fixes Change CommandEventArgs to be based on HandledEventArgs instead of CancelEventArgs #4023

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 issue #4023 by replacing the use of CancelEventArgs with HandledEventArgs in various command event handlers across the Terminal.Gui examples. The key changes include:

• Updating assignments from e.Cancel to e.Handled for consistent event handling.
• Revising inline comments to reflect the new property.
• Modifying the ReactiveExample command event argument types (with one potential inconsistency noted).

Reviewed Changes

Copilot reviewed 51 out of 51 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Examples/UICatalog/Scenarios/SimpleDialog.cs	Replaced e.Cancel with e.Handled in dialog acceptance.
Examples/UICatalog/Scenarios/Shortcuts.cs	Updated event handler assignments from Cancel to Handled.
Examples/UICatalog/Scenarios/MessageBoxes.cs	Changed event assignment from e.Cancel to e.Handled.
Examples/UICatalog/Scenarios/Menus.cs	Systematic change from e.Cancel to e.Handled in menu actions.
Examples/UICatalog/Scenarios/LineDrawing.cs	Replaced e.Cancel with e.Handled in color prompting events.
Examples/UICatalog/Scenarios/Generic.cs	Adjusted comment and event property from e.Cancel to e.Handled.
Examples/UICatalog/Scenarios/FileDialogExamples.cs	Changed file dialog event handling from Cancel to Handled.
Examples/UICatalog/Scenarios/Editors/PosEditor.cs	Updated event property from e.Cancel to e.Handled in editor init.
Examples/UICatalog/Scenarios/Editors/DimEditor.cs	Replaced e.Cancel with e.Handled in dimension editor events.
Examples/UICatalog/Scenarios/Dialogs.cs	Multiple updates of e.Cancel to e.Handled in dialog event handlers.
Examples/UICatalog/Scenarios/CharacterMap/CharacterMap.cs	Replaced e.Cancel with e.Handled when handling the ENTER key.
Examples/UICatalog/Scenarios/Buttons.cs	Numerous updates replacing e.Cancel with e.Handled in button events.
Examples/UICatalog/Scenarios/Bars.cs	Modified event handling for menu shortcuts and status bar actions.
Examples/UICatalog/Scenarios/AllViewsTester.cs	Changed event handling property from Cancel to Handled.
Examples/UICatalog/Scenarios/Adornments.cs	Updated window close event to use e.Handled instead of e.Cancel.
Examples/SelfContained/Program.cs	Revised comment and event property from e.Cancel to e.Handled.
Examples/NativeAot/Program.cs	Changed event handling from e.Cancel to e.Handled for login error events.
Examples/Example/Example.cs	Updated acceptance logic replacing e.Cancel with e.Handled.
Examples/CommunityToolkitExample/LoginView.cs	Revised event handling to use e.Handled instead of e.Cancel.
Examples/ReactiveExample/LoginViewModel.cs	Changed ReactiveCommand event args type from HandledEventArgs to CancelEventArgs (potential inconsistency).

[tig]

Modifying the ReactiveExample command event argument types (with one potential inconsistency noted).

I had to do this because I couldn't get the reactive sample to build otherwise.