Fix async race condition in the tree

[solomatov]

This PR fixes #82290

The following was done:

• Introduced _isDisposed field on the ExplorerItem class
• Set it to true when children are deleted from the active tree
• Check that nodes are not disposed in the code revealing resource, and if they are disposed start over

[isidorn]

Thank you for the PR and your investigation from #82290
At the end of the day you are checking if the item got disposed and if yes start over. In theory none of the items should be disposed which are in the model, so we can try to fix this one level sooner?
Maybe instead of introducing the whole dispose logic we should fire the onDidSelectResource with a timeout of 0 here. Or react with a timeout here

@solomatov did you also check that your fix trully fixes the issue
@joaomoreno can you also take a look, would be interested in what you have to say. Thanks

[joaomoreno]

Overall this makes sense. Given that the model has a forgetChildren, it serves as a great starting point to remember that those children should not be give to the tree.

[solomatov]

Added a retry count in a new commit.

[solomatov]

@isidorn Concerning the applicability of this, my understanding of the problem is that children are loaded asynchronously, and we can't do anything with it. It's nodejs, and if we use sync calls, UI wouldn't be so responsive.

[isidorn]

Let's go with this PR and push it to insiders to get user feedback.
The code is not so nice, but it is a decent workaround until we get something better.
Thank you for your PR @solomatov