[API] Add LLink.resolve static / instance methods (#974)

- `LLink.resolve`: Resolves all IDs on the link to their respective
objects (node IDs, slot indexes)
- `LinkNetwork.getLink`: a more concise pattern to resolve links

src/LGraph.ts

@@ -1174,6 +1174,17 @@ export class LGraph implements LinkNetwork, Serialisable<SerialisableGraph> {
     }
   }
 
+  /**
+   * Finds the link with the provided ID.
+   * @param id ID of link to find
+   * @returns The link with the provided {@link id}, otherwise `undefined`. Always returns `undefined` if `id` is nullish.
+   */
+  getLink(id: null | undefined): undefined
+  getLink(id: LinkId | null | undefined): LLink | undefined
+  getLink(id: LinkId | null | undefined): LLink | undefined {
+    return id == null ? undefined : this._links.get(id)
+  }
+
   /**
    * Returns a reroute by ID, or `undefined` if the ID is `null` or `undefined`.
    * @param id ID of reroute to return