TreeDataProvider.getChildren is called on extension activation

[weinand]

Testing #27467:

In the extension's activation I register the TreeDataProvider like this:

vscode.window.registerTreeDataProviderForView('loadedScriptsExplorer', new ScriptsExplorer());

When the extension gets activated, TreeDataProvider.getChildren is called even if the tree section "Loaded Scripts" in the Navigator is still collapsed:

I would expect that TreeDataProvider.getChildren is called when I expand the "Loaded Scripts" section in the navigator.