Improve connecting link logic (#697)

### Current

- Connections are disconnected the moment a link starts being dragged
- Reseating a connection where it came from creates a new connection
- If the process is somehow interrupted, the links are already gone

### Proposed

- Connection is disconnected after a new connection is made
- Rendering is bypassed for the link segment being moved
- Does nothing if dropping a link exactly where it came from
- Adds early return when trying to connect a node to itself

src/utils/collections.ts

@@ -1,4 +1,5 @@
-import type { Positionable } from "../interfaces"
+import type { ConnectingLink, Positionable } from "../interfaces"
+import type { LinkId } from "@/LLink"
 
 import { LGraphNode } from "@/LGraphNode"
 
@@ -35,3 +36,13 @@ export function findFirstNode(items: Iterable<Positionable>): LGraphNode | undef
     if (item instanceof LGraphNode) return item
   }
 }
+
+/** @returns `true` if the provided link ID is currently being dragged. */
+export function isDraggingLink(linkId: LinkId, connectingLinks: ConnectingLink[] | null | undefined): ConnectingLink | undefined {
+  if (connectingLinks == null) return
+
+  for (const connectingLink of connectingLinks) {
+    if (connectingLink.link == null) continue
+    if (linkId === connectingLink.link.id) return connectingLink
+  }
+}