We've established that \Ibexa\AdminUi\UI\Module\ContentTree\NodeFactory::isPreviewable is called for every node of Content Tree loaded by load-subtree (ContentTreeController::loadSubtreeAction) controller and its execution has a very high impact on the performance of Content Tree if it has hundreds of items (which is possible even for mid-sized instances, given the default depth is 10).

We need to find a way to optimize/cache this.

Steps to reproduce

1. Create a clean instance, ideally of Ibexa Commerce to have the biggest overhead and ideally using Redis.
2. Create many content items that are displayed in Content structure tree (test-fixtures - TBD if it's enough)

Actual result

Observe that it takes long time to load the Content Tree

Expected result

Content Tree loads faster (there's a lot of features in 4.6 so it still will be slower than 4.5).