views: fix focus ring invisible issue in LayoutManagerBase

FocusRing was not laid out by LayoutManagerBase because it reports a zero preferred size. This patch marks FocusRing as a "decorative view",
such that:

* it has the View property kIsDecorativeViewKey set to true.
* its visibility is respcted by LayoutManagerBase. i.e. the layout
  manager's proposed visibility is disregarded.
* its Layout() is always invoked during layout.

Bug: b/325029896
Change-Id: I02daf708405cb3f9db777293107f8cd516929b0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5293541
Commit-Queue: Keren Zhu <kerenzhu@chromium.org>
Reviewed-by: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1260680}