Add start function to nodegit Tree.walk return type (#35698)

* Add start function to Tree.walk return type

* Add test

types/nodegit/nodegit-tests.ts

@@ -13,6 +13,8 @@ const id = new Git.Oid();
 const ref = new Git.Reference();
 const tree = new Git.Tree();
 
+tree.walk().start();
+
 // AnnotatedCommit Tests
 
 Git.AnnotatedCommit.fromFetchhead(repo, "branch_name", "remote_url", id).then((annotatedCommit) => {

types/nodegit/tree.d.ts

@@ -58,7 +58,12 @@ export class Tree {
     /**
      * Recursively walk the tree in breadth-first order. Fires an event for each entry.
      */
-    walk(blobsOnly?: boolean): NodeJS.EventEmitter;
+    walk(blobsOnly?: boolean): NodeJS.EventEmitter & {
+        /**
+         * Start walking the tree and emitting events. This should be called after event listeners have been attached.
+         */
+        start: () => void;
+    };
     /**
      * Return the path of this tree, like /lib/foo/bar
      *