WorkspaceEdit: confirmation preview does not reflect the create content

Testing #161809 ``` let disposable = vscode.commands.registerCommand('workspaceedit-test.helloWorld', () => { const edit: vscode.WorkspaceEdit = new vscode.WorkspaceEdit(); const folders = vscode.workspace.workspaceFolders; if (!folders || folders.length === 0) { vscode.window.showInformationMessage('Open a folder first'); return; } const newFile = vscode.Uri.joinPath(folders[0].uri, 'foo.txt'); edit.createFile(newFile, { overwrite: true, contents: new TextEncoder().encode("Hello World\nOne more line") }, { label: 'New text', needsConfirmation: true } ); const range = new vscode.Range(0, 0, 0, 5); const snippetString = new vscode.SnippetString('Rocket'); snippetString.appendChoice(['A', 'B', 'C'], 1); const newSnippetEdit = new vscode.SnippetTextEdit(range, snippetString); edit.set(newFile, [newSnippetEdit]); vscode.workspace.applyEdit(edit); }); ``` - create a new file `foo.txt` with a new content - applies a snippet string - requires confirmation - run the first time:  - run the second time, after accepting the first  :bug: the confirmation preview shows the previous file content, not the new file content (`Hello`)