Add Reroutes (#301)

* Add Reroute

- Initial Reroute implementation
- LLink and Reroute both implement the new LinkSegment interface
- LinkSegments can have a parentId, which always points to a Reroute

* Narrow TS type of schema v0.4 extras

* Add reroutes to schema 0.4

Use extras.reroutes to store additional data

* Add Reroute POC to LLink

* Add Reroute rendering

* Add Reroute context menu - Delete Reroute

* Update delete selected - include reroutes & groups

* Add Reroute select & move

* Include reroutes in area-select

* Move disconnect link logic to LLink

* Add Reroute connect

* nit

* Add Reroute support - connecting links

* Add Add Reroute from link menu (menu)

* nit

* Add shift-drag from reroute to add new link

* Prevent Reroutes from disappearing

Add keepReroutes option to prevent Reroute GC

* Add fourth param to connectInputToOutput

* Allow both connecting in/out to be null

* Move ConnectingLink start pos to Reroute

* Add link render options

* Refactor renderLink - spline / bezier

* Refactor renderLink - linear, straight

* Fix centre points on all link types

Improves link render time

* [Refactor] Generic recursive interface / flat set

* nit

* Allow Reroutes to be members of groups

* Start links from the closest reroute

For the "shift-click drag link from link" feature

* Add Reroutes using alt-click on link paths

* nit - Refactor

* nit - Refactor

* Fix reroute deselect UX

Temporary workaround

* Add Reroute link centre-marker handling

* Add optional link arrow markers

Add enum for link markers
-> Pointing the way forward ->
Set default centre marker to arrow

* Add module export: LinkMarkerShape

* Add link arrow direction for all link types

* Add Reroute auto-swivel with custom curves

* Add state switch to disable reroutes

Works at root of all canvas interactions, should leave existing reroutes untouched but invisible until e.g. links are edited / changed.

* Fix cannot deselect when reroutes disabled

* Include reroutes in select-all

src/utils/collections.ts

@@ -0,0 +1,18 @@
+import type { Parent } from "../interfaces"
+
+/**
+ * Creates a flat set of all items by recursively iterating through all child items.
+ * @param items The original set of items to iterate through
+ * @returns All items in the original set, and recursively, their children
+ */
+export function getAllNestedItems<TParent extends Parent<TParent>>(items: ReadonlySet<TParent>): Set<TParent> {
+    const allItems = new Set<TParent>()
+    items?.forEach(x => addRecursively(x, allItems))
+    return allItems
+
+    function addRecursively(item: TParent, flatSet: Set<TParent>): void {
+        if (flatSet.has(item)) return
+        flatSet.add(item)
+        item.children?.forEach(x => addRecursively(x, flatSet))
+    }
+}