message: If a dirty file is open in two splits, allow closing one with :q
  This isn't perfect, as we can't account for the case that a file is open in another unsurfaced tab.
  Refs
diff: @@ -27,7 +27,12 @@ export class QuitCommand extends node.CommandBase {
  }
  async execute(): Promise<void> {
  - if (this.activeTextEditor!.document.isDirty && !this.arguments.bang) {
  + // NOTE: We can't currently get all open text editors, so this isn't perfect. See #3809
  + const duplicatedInSplit =
  + vscode.window.visibleTextEditors.filter(
  + editor => editor.document === this.activeTextEditor!.document
  + ).length > 1;
  + if (this.activeTextEditor!.document.isDirty && !this.arguments.bang && !duplicatedInSplit) {
  throw error.VimError.fromCode(error.ErrorCode.E37);
  }
  