message: Add ids for divs for side-by-side component viewer
  Add an id attribute for divs when presented side-by-side in the component viewer.  This makes it easier to differentiate the two when debugging.
  Fixes
diff: @@ -176,11 +176,14 @@ function getUrlResolver(options: IRouteOptions): IUrlResolver {
  }
  // Invoked by `start()` when the 'double' option is enabled to create the side-by-side panes.
  -function makeSideBySideDiv() {
  +function makeSideBySideDiv(divId?: string) {
  const div = document.createElement("div");
  div.style.flexGrow = "1";
  div.style.border = "1px solid lightgray";
  div.style.position = "relative"; // Make the new <div> a CSS stacking context.
  + if (divId) {
  + div.id = divId;
  + }
  return div;
  }
  @@ -223,8 +226,8 @@ export async function start(
  let leftDiv: HTMLDivElement;
  let rightDiv: HTMLDivElement;
  if (double) {
  - leftDiv = makeSideBySideDiv();
  - rightDiv = makeSideBySideDiv();
  + leftDiv = makeSideBySideDiv("sbs-left");
  + rightDiv = makeSideBySideDiv("sbs-right");
  div.append(leftDiv, rightDiv);
  }
  