Fixes #3695 - Add event handlers for Accept in ColorPicker text fields

[tznind]

Fixes

• Fixes ColorPicker should apply changes on Accept as well as OnHasFocusChanged #3695

Proposed Changes/Todos

Make Accept (default key Enter) in text boxes update color selection similarly to focus change events.

@tig I have removed the .NewValue if check as I'm not sure what it means on a focus changing event. Presumably the new value is supposed to indicate whether it is entering or leaving? either way the behaviour seems correct regardless.

I've also removed the -= event handler removals. The reason is because we are now using anonymous delegate (s,_)=> for both Accept and FocusChange.

I don't think they are needed anyway as the lifecycle of the view at that point is where they are Disposed anyway so no events should get raised and they will go out of scope and get cleaned up anyway.

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

[tig]

@tig I have removed the .NewValue if check as I'm not sure what it means on a focus changing event. Presumably the new value is supposed to indicate whether it is entering or leaving? either way the behaviour seems correct regardless.

Correct. For HasFocusChanging/HasFocusChanged e.NewValue == true indicates what we used to think of as "enter".