Adjust behavior of all close tab commands

[Hanksha]

Fixes #7268, adjust behavior of all close tab commands so that they respect the widget.title.closable property.

What it does

This PR improves the close tab commands so that they take into account the widget.title.closable property. It means that a widget cannot be closed using any of the commands if widget.title.closable === false.

The behavior is as follow:

• Close and Close Tab in Main Area are enabled when the current widget is closable
• Close Others and Close Other Tabs in Main Area are enabled if at least one other widget is closable
• Close All and Close All Tabs in Main Area enabled if at least one widget is closable
• Close to the Right is enabled if at least one widget to the right is closable

How to test

I added a sample view to the examples so you can open the Sample Unclosable View and toggle the checkbox in it to set title.closable and try the logic described above.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[akosyakov]

As far as I understood this PR only tries to prevent closing from user perspective, from programming perspective one can still close. I think it is reasonable, just checking.

[Hanksha]

@akosyakov Yes it only affects the commands, one can still close the tab programmatically using the ApplicationShell methods.

[akosyakov]

@Hanksha fyi https://help.github.com/en/enterprise/2.16/user/github/managing-your-work-on-github/closing-issues-using-keywords

[spoenemann]

Great! A few remarks.

[westbury]

I have tested this and it works fairly well. I did note the following:

1. When a view is not closable (and there are other closable views), the action 'Close Others' is disabled. I would expect it to be enabled.
2. It looks like 'close others' should only close views within the same location. We need to be sure this is all consistent.

[westbury]

This function is going to get rather big if lots of stuff is added to it. Also it is not clear which lines relate to which example. Same comment applies to api-samples-contribution. It seems to me we should have a single function call here for each example, so here we have just

bindDynamicLabelProvider(bind);
bindUnclosableView(bind);

Then have a folder for each example where these functions are implemented. I know this is not how it was set up before, but now you are adding the second example it would be helpful if you were able to improve the structure here.

[Hanksha]

Ok I see what you mean, I'll improve that.

[Hanksha]

I gave it a try, tell me what you think.

[Hanksha]

1. When a view is not closable (and there are other closable views), the action 'Close Others' is disabled. I would expect it to be enabled.
2. It looks like 'close others' should only close views within the same location. We need to be sure this is all consistent.

1. I cannot reproduce it, "Close Others" is disabled only when there are no other closable views.
2. Yes that's right, I changed it to behave that way.

[akosyakov]

@spoenemann please merge

[westbury]

1. cannot reproduce it, "Close Others" is disabled only when there are no other closable views.

I was misunderstanding what was the same or a different area. It's working fine.

[westbury]

Looks great. Thanks also for changing the view title from 'Sample'. I forgot to mention that but you did it anyway. I appreciate your keeping the examples package tidy too, as that was not really part of this PR.