Allow debug widgets to get updated when not visible

[federicobozzini]

What it does

This adds a property alwaysUpdate to TreeWidget that can be used to force a widget to update even when not visible or attached. This property is used by the Widgets showing debug information to get rendered even when not visible.

Fixes: #8639.

How to test

The easiest way to test this, would be to switch the active panel right after a debug session is terminated. This would normally prevent the debug information to get cleared, because of debug widgets not being visible. With this PR the debug widgets are correctly cleared when the debug session is terminated.

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

[kittaakos]

VS Code does it differently. When the debug session is over and the debug view was not active, Code leaves the trees untouched. The trees are cleaned up only when the debug view is activated again and there is not active debug session. See the screencast

Why do not we do the same? If not necessary, let's not introduce another property on the tree-widget just because you want to work around something. (Especially, you can customize this behavior in your extension.) Can we handle this issue with onAfterShow on the DebugSessionWidget?

[kittaakos]

TreeWidgets should be customized via TreeProps and not the way you did.

[federicobozzini]

Why do not we do the same? If not necessary, let's not introduce another property on the tree-widget just because you want to work around something. (Especially, you can customize this behavior in your extension.)

Actually I've noticed that this issue is also present in vanilla Theia. All it takes to see it is too start a debug session, switch the active panel and then stop the active debug session by using Shift + F5. Once you go back to the Debug panel you can see that the debug panel is not correctly cleared.

Can we handle this issue with onAfterShow on the DebugSessionWidget?

@kittaakos I think this is a brilliant idea.

[federicobozzini]

Before this change:

After this change:

[vince-fugnitto]

@federicobozzini the changes work very well for me and provide a much better debugging experience, similarly to vscode:

1. open a *spec.ts file.
2. start debugging with the run mocha test configuration.
3. open the explorer.
4. return to the debug view once the session has ended.
5. the debug view is properly updated, while on master it is not.

[vince-fugnitto]

@federicobozzini do you need help merging?

[federicobozzini]

@vince-fugnitto Yes, please. I don't have the permissions to merge this PR.