Add breadcrumbs to the selection panel

[abey79]

The enclosing context of the selected item should be displayed as breadcrumbs to facilitate the navigation. This issue is about the design and implementation of this feature.

####New context from Dec '24
We are implementing undo, and want to get rid of the selection panel errors navigations ←→.
Despite the arrows being ambiguous UX element, it is being used to navigate via selected panels (especially when users click somewhere where they did not want to go, so they go 'back' to the previous view).
Assumption is that breadcrumbs will be a better navigation support for this as well as a more familiar ux pattern.

Design issues

Proposal based on Marten's sketches:

This will also allow to remove some of the elements in the selection panel as they will become redundant,
merge parent and in view in blueprint, remove in view

Implementation issues

• implement the capability to walk the hierarchy up
• implement the breadcrumb in selection panel

cc @jleibs @emilk

[gavrelina]

Upd:

• we decided to use first entity letters instead of entity icons, as they give a better hint on what is the the actual name of the entity
• and use a little store icon for the root in the streams
• for entities in BP : we merge Parent + Entity and remove In view

[emilk]

• Most of it done in Add selection hierarchy breadcrumbs #8319

Still need to properly sync "projection" entities with the blueprint tree panel.

The problem with projections include:
A) I don't know what the logic is for how they are displayed in the blueprint tree view
B) I don't know if how they are displayed in the blueprint tree view is a good model to follow
C) If it is a good model to follow, I don't know how to follow it

I don't feel confident moving forward with this without a few more motivating examples of projections.

[jleibs]

A) I don't know what the logic is for how they are displayed in the blueprint tree view

This happens here:

rerun/crates/viewer/re_blueprint_tree/src/blueprint_tree.rs

Lines 390 to 406 in 76d4663

	// Show 'projections' if there's any items that weren't part of the tree under origin but are directly included.
	// The latter is important since `+ image/camera/**` necessarily has `image` and `image/camera` in the data result tree.
	let mut projections = Vec::new();
	result_tree.visit(&mut |node| {
	if node
	.data_result
	.entity_path
	.starts_with(&space_view.space_origin)
	{
	false // If it's under the origin, we're not interested, stop recursing.
	} else if node.data_result.tree_prefix_only {
	true // Keep recursing until we find a projection.
	} else {
	projections.push(node);
	false // We found a projection, stop recursing as everything below is now included in the projections.
	}
	});

B) I don't know if how they are displayed in the blueprint tree view is a good model to follow

I'm probably biased as it was my idea, but I'm not deeply attached to it. If somebody has a more intuitive model for thinking about paths that are rooted above the origin, I'm totally open to it.

C) If it is a good model to follow, I don't know how to follow it

You can combine the snippet from above, with the logic to resolve an Item::DataResult

Following the pattern here:

rerun/crates/viewer/re_selection_panel/src/selection_panel.rs

Lines 261 to 266 in 76d4663

	let entity_path = &instance_path.entity_path;
	let query_result = ctx.lookup_query_result(*view_id);
	let data_result = query_result
	.tree
	.lookup_result_by_path(entity_path)
	.cloned();

[emilk]

Closed; next step in:

• Sync selection panel breadcrumbs with blueprint tree hierarchy #8342