`ComputedUpdater` doesn't reevaluate the `enabled` property in an `IAction` object

[RomanTsukanov]

https://plnkr.co/edit/GC9hytDLvNTZsdEZ

In this example, a custom Clear Survey button is added to the toolbar. ComputedUpdater is used to activate the button when the survey is not empty. However, this doesn't work.

Steps to reproduce:

1. Click the "Clear Survey" button. The button becomes disabled, which is fine.
2. Add a new question to the survey. Expected result: The "Clear Survey" button becomes enabled again, since the survey contains an element. Current result: "Clear Survey" is disabled.