Improve the handling of out-of-DataResultTree data result items

[abey79]

Background

In #5342, a DataResultNodeOrPath structure was introduced in the blueprint tree UI code address the fact that we want the tree to display $origin even if that actual entity path is not part of the data results. That happens for example when the query is set to something like + $origin/sub_entity/**. In that case, for the purpose of tree UI code, $origin would be a "placeholder" node.

Problem

This has unfortunately wider ranging implications. Since the "placeholder" origin is displayed, it can be selected. However, it is considered "invalid" by some other part of the code (namely ViewportBlueprint::is_item_valid()), which in turns preclude said item to be selected. This caused #5683.

This bug was fixed in #5743 with a hack that is probably fragile (aka tightly coupled to what we want to display in the blueprint tree).

Solution

As per @jleibs's comment below:

• the query result computed in the AppState::show() should always include the entire $origin subtree
• items that are in the origin subtree but not actual results from the query should exist, have their tree_prefix_only flag set, be displayed in the blueprint tree, but not in the actual space view
• it should then be possible to get rid of the DataResultsNodeOrPath enum
• the fix from Fix issue where "placeholder" DataResults couldn't be selected #5743 should be reverted

[jleibs]

The place where we invoke is_item_valid is only a couple lines above the place where we generate the query results. I suspect if move this check to after we run the query, we can use actual query results rather than using the filter. This would let us unify the behavior by making the query results themself the arbiter of whether something is valid.