message: Fix getSplitSingleViewportCommandDef() to properly
  get the current number of content views
  in the current Frontstage.
diff: @@ -150,12 +150,12 @@ export function getSplitSingleViewportCommandDef() {
  const commandId = "splitSingleViewportCommandDef";
  return new CommandItemDef({
  commandId,
  - iconSpec: new ConditionalStringValue(() => IconSpecUtilities.createWebComponentIconSpec(1 === FrontstageManager.activeFrontstageDef?.contentControls?.length ? splitVerticalIconSvg :singlePaneIconSvg), [SyncUiEventId.ActiveContentChanged]),
  - label: new ConditionalStringValue(() => 1 === FrontstageManager.activeFrontstageDef?.contentControls?.length ? "Split Content View" : "Single Content View", [SyncUiEventId.ActiveContentChanged]),
  + iconSpec: new ConditionalStringValue(() => IconSpecUtilities.createWebComponentIconSpec(1 === FrontstageManager.activeFrontstageDef?.contentGroup?.getContentControls().length ? splitVerticalIconSvg :singlePaneIconSvg), [SyncUiEventId.ActiveContentChanged]),
  + label: new ConditionalStringValue(() => 1 === FrontstageManager.activeFrontstageDef?.contentGroup?.getContentControls().length ? "Split Content View" : "Single Content View", [SyncUiEventId.ActiveContentChanged]),
  execute: async () => {
  // if the active frontstage is only showing an single viewport then split it and have two copies of it
  const activeFrontstageDef = FrontstageManager.activeFrontstageDef;
  - if (activeFrontstageDef && 1 === activeFrontstageDef.contentControls?.length &&
  + if (activeFrontstageDef && 1 === activeFrontstageDef.contentGroup?.getContentControls().length &&
  activeFrontstageDef.contentControls[0].viewport) {
  const vp = activeFrontstageDef.contentControls[0].viewport;
  if (vp) {
  @@ -207,7 +207,7 @@ export function getSplitSingleViewportCommandDef() {
  const contentGroup = new ContentGroup(contentGroupProps);
  await FrontstageManager.setActiveContentGroup(contentGroup);
  }
  - } else if (activeFrontstageDef && 2 === activeFrontstageDef.contentControls?.length &&
  + } else if (activeFrontstageDef && 2 === activeFrontstageDef.contentGroup?.getContentControls().length &&
  activeFrontstageDef.contentControls[0].viewport) {
  const vp = activeFrontstageDef.contentControls[0].viewport;
  if (vp) {
  