AI 146238: ADT #1761064: Properly refresh UiTreeBlock when SDK is reloaded.

  The fix I did last week was just refreshing the UiRootNode
  but it turns out we need to refresh the DescriptorFilters too
  (since they are null when there's no SDK.) So the old fix was
  wrong, what we need is to generate a new tree model when the
  SDK is reloaded.
  BUG=1761064

Automated import of CL 146238