flyout: Drilldown's hovers should update when FlyoutController is null

This CL fixes a bug that was causing drilldown's hover state to be not
changing when `FlyoutController` was null. This was because we were
relying on `FlyoutController`'s `updateHighlights()` method to update
the hover state.

We move `updateHighlights()` to `HierarchicalMenuController`, as it's
used for both drilldowns and flyouts.

Bug: 450453191
Change-Id: Ic36b39cf9e7c3e33a7908f9490f9758d67de2cb9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7025031
Commit-Queue: Masa Fujita <massan@google.com>
Reviewed-by: Sinan Sahin <sinansahin@google.com>
Cr-Commit-Position: refs/heads/main@{#1529238}