Fix arrow layout in landscape and hide if scroll is disabled

- Add missing constraint in landscape layout that had resulted in overlap with
  text with a larger display/font size
- If scrolling is not allowed for the media host, always hide the pager arrows

Bug: 383974508
Flag: com.android.systemui.media_carousel_arrows
Test: atest MediaCarouselControllerTest
Test: manual - check phone landscape with max size

Change-Id: Ib0e860cbbb1f1207de43b1cd54b377fd3f4fdc83