Convert LoadedScriptsView to use compact tree

[weinand]

Today the LoadedScriptsView implements its own "compact tree representation" when folders only have single children.
Since VS Code's tree view now supports a "compact tree representation", LoadedScriptsView should use that.

[weinand]

With help from @isidorn and @joaomoreno the LoadedScriptsView is now based on the WorkbenchCompressibleObjectTree.