Add an heuristic to list all entity sub-trees with content compatible with a given space view class

[abey79]

In order to propose meaningful entity paths, #4848 made use of all_possible_space_views(), which is totally overkill for the purpose. Ideally, there would be a simpler API to list all possible entity sub-trees which contain some content that can be visualised by a given space view class.

[Wumpf]

FYI: In an upcoming pr this changes to a filter based on default_created_space_views which is a smaller set but similarly problematic. In fact it's a much slower operation (but due to recent changes decently fast so that we don't mind running it again while this property is edited)