src/goExplorer.ts: create opened files if they do not exist

For #2049

Change-Id: Iaa4c5cf67d44f97f8fe4bd0e49a897cc5d4d9624
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/391256
Trust: Jamal Carvalho <[email protected]>
Run-TryBot: Jamal Carvalho <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: kokoro <[email protected]>

Author: jamalc

src/goExplorer.ts

@@ -82,6 +82,9 @@ export class GoExplorerProvider implements vscode.TreeDataProvider<vscode.TreeIt
 
 	private async open(item: EnvTreeItem) {
 		if (typeof item.file === 'undefined') return;
+		const edit = new vscode.WorkspaceEdit();
+		edit.createFile(item.file, { ignoreIfExists: true });
+		await vscode.workspace.applyEdit(edit);
 		const doc = await vscode.workspace.openTextDocument(item.file);
 		await vscode.window.showTextDocument(doc);
 	}