Highlight items related to the selected items

[abey79]

Current situation

Currently, hovering on an item highlights a number of other, related items. This helps to understand the relationships between various pieces of data.

In contrast, selecting an item only highlights the selected item, without providing any kind of feedback on what other items might be related.

Notable exception: selecting a group in blueprint tree highlights the entire corresponding sub-tree in the corresponding space view (but not in other space views, even if they contains the same entities). (edit: groups are a thing of the past now)

Proposed change

Motivation:

• make it easier to locate in the blueprint tree and/or streams tree an item that is selected in the space view
• help understand relationship between various pieces of data
• make what happens in (spatial) space views and the rest of the UI more consistent.

When a data-related item (data result, entity regardless of context, etc.), the following related items should be highlighted in some muted way:

• the selected item(s) sub-tree(s) (as figma does)
• the selected item(s) counterpart(s) in other contexts (same entity in different space view, or in the data store)
• the selected item(s) counterpart(s)'s sub-tree(s)

Specifically, we propose to exclude the selected item(s) ancestor path from the set of highlighted related items, and favour the mechanism in #5256

For the subdued highlighting, a good starting point appears to be the selection colour at 50% alpha (prototyped and looks OK in spaces views).

Design document: https://www.figma.com/file/D667sz3Q0jKas5pLbbFyp3/Hover%2FSelection%3A-Related-Items-Highlighting?type=whiteboard&node-id=0%3A1&t=OeLQwj4WNF3hBNDK-1

cc @Wumpf

[abey79]

cc @gavrelina