Avoid extra call to Iterable.map (microsoft#163902)

We loop through the nodes, so can simply do the map inside of the loop instead of making this extra call

Author: mjbvz

src/vs/base/browser/ui/tree/indexTreeModel.ts

@@ -526,12 +526,12 @@ export class IndexTreeModel<T extends Exclude<any, undefined>, TFilterData = voi
 
 		const childElements = treeElement.children || Iterable.empty();
 		const childRevealed = revealed && visibility !== TreeVisibility.Hidden && !node.collapsed;
-		const childNodes = Iterable.map(childElements, el => this.createTreeNode(el, node, visibility, childRevealed, treeListElements, onDidCreateNode));
 
 		let visibleChildrenCount = 0;
 		let renderNodeCount = 1;
 
-		for (const child of childNodes) {
+		for (const el of childElements) {
+			const child = this.createTreeNode(el, node, visibility, childRevealed, treeListElements, onDidCreateNode);
 			node.children.push(child);
 			renderNodeCount += child.renderNodeCount;