Adding a carent in the scrim

> Caret is only visible when the accessibility is enabled
> It is visible in NOTMAL and OVERVIEW state and moves out of the
  scrim along with the scrim.
> Acts as an accessible target for various options

Bug: 78172350
Bug: 79215734
Change-Id: I8a968b67e36901859649546295f6491d49cc9ce9